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Old 11-22-2019, 09:14 AM
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Intermittent Engine "hum" 3.6

Hello all, thanks for taking a read and seeing if you can help!

2013 JKU 40,000 miles...

I have a strange and intermittent high pitch hum that I can't track down. It's not as high pitched as a squeak or squeal, if that makes any sense. It only happens while moving and it will bounce back and forth between 2 different audible notes or tones...it does not get higher/lower equally with rpm, speed or gear but does change tone between the 2 sounds...think holding down one piano key and then jumping up a few piano keys and holding that down...It does not happen every day but I would say it happens 3-4 times a week. Anytime I have heard it I have been just driving around town 10-35 mph. It lasts for maybe 10-30 seconds, depending on how much stop and go traffic i'm in. I know how hard it is to diagnose sounds as being described on the internet, but I appreciate you reading this! I will try to get a video of it next time and get it loaded up here.

Thanks in advance!

Dan

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Old 11-22-2019, 09:58 AM   #2
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Because it’s intermittent and not specific to speed or RPM it’s probably not tires, gears, or drive shaft.

Instead, what has been installed on the Jeep that would cause wind noise? Light bars, roof rack, straps of any kind? Different top, freedom panels loose, side view mirrors, antenna... Loose fenders or plastic trim..,

Aerodynamic changes will cause what you are describing.

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Old 11-22-2019, 10:19 AM
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I have made ALOT of aerodynamic changes in the last year to the jeep, but this intermittent noise has come on 3+ months after the changes were made. I've had other jeeps in the past with light bar wind noise and this is not that. It is so irregular that it can't be, if it were aerodynamic it would be more consistent and change in loudness and possibly tone with speed=more wind. I have also ran "naked" many times since making the aerodynamic changes and this sound was not there. The sound appears to be coming from the engine compartment and possibly from the driver side almost directly in front of the steering wheel.

I REALLY appreciate the feedback and idea, this just doesn't seem to be an aerodynamic issues in this case. Thanks again!
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Old 11-22-2019, 03:08 PM   #4
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OK - check that all of those bolt ons are still tight. Plastic fenders, grill inserts, fender liners...

Directly in front of the steering wheel is primarily brake booster and ABS system. Both of those could cause noise in the form of vacuum leaks, air in the brake / ABS system but would be strange that this only occurs while driving and not in park with engine idling. I mention ABS module only because I had an ABS module on a BMW that made similar strange noises when it was failing. Valving and seals would vibrate...

Not so likely though as you would expect rough idle, poor brake performance or warning light if either of the above.
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Old 11-22-2019, 03:12 PM   #5
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Also meant to mention serpentine belt and pulleys.
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Old 11-22-2019, 04:14 PM   #6
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Old 11-22-2019, 06:09 PM
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Also meant to mention serpentine belt and pulleys.
At this point I'm not ruling anything out...I am still going to be paying attention to anything that may be throwing weird aerodynamics.

As far as belts and pulleys, I would think that would happen anytime the engine is running though, and not just while moving. I keep coming around to some sort of a vacuum leak.

I'm not trying to be dismissive AT ALL, I'm just talking...um errr, typing...my way through my thoughts. Thanks a million for continuing to throw ideas at me!
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Old 11-22-2019, 06:10 PM
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Old 11-25-2019, 09:32 AM
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Paid closer attention to it this weekend and got a few videos I will try to upload. It comes on at 25 mph, changes to a different tone at 35 mph and goes away at 45 mph.
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Old 11-25-2019, 09:43 AM
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I have no idea if these links will work...


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Old 11-25-2019, 09:45 AM
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Old 11-25-2019, 09:47 AM
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The top link you can hear the "note or tone" very loud, the bottom link you later in the video, before the turn when the jeep is slowing down, you can clearly hear that "note or tone" change that it does at about 35 mph.
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Old 11-25-2019, 12:25 PM   #13
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Hello all, thanks for taking a read and seeing if you can help!

2013 JKU 40,000 miles...

I have a strange and intermittent high pitch hum that I can't track down. It's not as high pitched as a squeak or squeal, if that makes any sense. It only happens while moving and it will bounce back and forth between 2 different audible notes or tones...it does not get higher/lower equally with rpm, speed or gear but does change tone between the 2 sounds...think holding down one piano key and then jumping up a few piano keys and holding that down...It does not happen every day but I would say it happens 3-4 times a week. Anytime I have heard it I have been just driving around town 10-35 mph. It lasts for maybe 10-30 seconds, depending on how much stop and go traffic i'm in. I know how hard it is to diagnose sounds as being described on the internet, but I appreciate you reading this! I will try to get a video of it next time and get it loaded up here.

Thanks in advance!

Dan
Hi Dan,
We understand why this may be frustrating. Are you considering having your dealer take a look? If so, please send our team a PM. We'd be happy to connect you with a Case Specialist to assist.
Alex
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Old 11-25-2019, 01:06 PM
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Hi Dan,
We understand why this may be frustrating. Are you considering having your dealer take a look? If so, please send our team a PM. We'd be happy to connect you with a Case Specialist to assist.
Alex
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No, I am not. I am outside of warranty and do not plan on having the dealer fix this issue.
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Old 11-25-2019, 02:04 PM   #15
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I am going to guess a bearing. Alternator or idler/tensioner. I had an alternator bearing fail on another vehicle and it made similar tones but lower tones.

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Old 11-25-2019, 02:15 PM
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I am going to guess a bearing. Alternator or idler/tensioner. I had an alternator bearing fail on another vehicle and it made similar tones but lower tones.

https://www.youtube.com/watch?v=PCEpV2q7re0
Thanks, Ill look into that!
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Old 11-25-2019, 02:16 PM
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I wish it would make the noise sitting still, that would make it so much easier to diag...and again, that statement points it back to aerodynamics...
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Old 11-25-2019, 07:10 PM   #18
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Your recordings were helpful to better understand!

Because this only happens when driving... My new suggestion - try looking for a slightly dragging brake pad. The sound in your recording is more like harmonic resonance. (Tuning fork).

Something like a wheel bearing or a brake pad and rotor could be resonating (like rubbing a wet finger on the top of a wine glass). As soon as you speed up or slow down outside of that particular speed range it changes frequency (unrelated to engine rpm) and apparently disappears.

Even a quick shot of brake cleaner could cause it to change or disappear and aid in identifying or eliminating one possible cause.
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Old 11-26-2019, 08:41 AM
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Your recordings were helpful to better understand!

Because this only happens when driving... My new suggestion - try looking for a slightly dragging brake pad. The sound in your recording is more like harmonic resonance. (Tuning fork).

Something like a wheel bearing or a brake pad and rotor could be resonating (like rubbing a wet finger on the top of a wine glass). As soon as you speed up or slow down outside of that particular speed range it changes frequency (unrelated to engine rpm) and apparently disappears.

Even a quick shot of brake cleaner could cause it to change or disappear and aid in identifying or eliminating one possible cause.
THANK YOU!!! That is exactly how, with a loss of words, I was trying to explain it! I will check the brakes as it is an easy one to rule out, like you said, with a shot of brake cleaner. Am I nuts to be leaning towards some sort of a vacuum leak?
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Old 11-26-2019, 09:33 AM   #20
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Vacuum leak - unlikely but possible. With engine running and the Jeep in park, make absolutely certain that you can’t recreate this sound. If it happens (at all) while stationary, then it’s engine related and could be vacuum, alternator, water pump bearing, belt, pulley, etc.

Otherwise it’s more likely driveline while the Jeep is rolling and could come from any place where two surfaces interface - brakes, bearings, u joint / drive shaft, transmission, transfer case, gears, etc. Check obvious items first like brakes and rotors, brake pad wear indicators, wheel spacers and lugs tight, fluids full - trans, transfer case and diff. You can also put a jack under the front axle and spin each wheel by hand...

Unfortunately, it can be so many different things and you will have to start eliminating what you can. We can really only make an educated guess based on the limited info provided
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