Originally Posted by Johnnyp
Its a 2011, just over 10k miles.
I do both mudding and rock crawling. I "think" this problem started BEFORE my first time mudding with this JK.
Hate to admit it, but I drive like a grandma.
Lining up my WAGs in the order I'd tackle them:
Mud/dirt in the alternator (a quick look is all that's needed)
All pulleys for the Serpintine belt (loosen the belt and spin stuff by hand to see how free everything is)
The belt itself - condition/tension (Try tighten it a hair. Wait and see)
I'm really stretching here but I'm suspecting the belt is a key to getting to the real problem.
The fact that this happens when you turn on the A/C makes me suspect the additonal load is affecting something for a second. It could be the belt slips and then heats up and grabs again. I know, this usually is a squealing sound but I've heard the grinding sound too.
Or, the additional load is causing a pully bearing to compain for a second. This could come from water (do much river fording?) cutting the bearing lubrication or just plain old premature failure.
If the belt is glazed and shiny I'd swap the bugger and call it a day until it happens again - if it does.
Or just do nothing until the problem stops being sporatic. Usually the option most take.