I would definitely turn down the gain. If you can turn the gain down, and the noise goes away, or is minimal, then, turn up your stereo to the maximum listening level, and check for good sound quality without distortion. One problem seems that maybe you have your gains set too high.
Then, check to see if you hear the buzz on the CD player, and other sources on your HU, such as AUX, Radio, internal SD card, etc. This way you can isolate what source might be causing the noise interference. I would definitely purchase high quality RCA cables.
Some of the cheaper stereo's have interference problems. The best thing to do is to make sure all your units are properly grounded. Check that your engine grounds are connected properly too. There is a flat ground cable behind the engine, connected to the top of the firewall, that splits into two cables. One side connects to the manifold. The other cable goes to your negative battery cable at the engine block. This makes sure that your tub and firewall are properly grounded. Then, inside the vehicle, behind the stereo, there is also another ground cable, that connects behind the instrument panel or sometimes it is on the firewall. You can move it around and maybe find a better ground point that may help to reduce or eliminate the noise. You might want to check if it is actually connected. Sometimes, this cable is removed, or not grounded to the chassis. This was the case for me after my stock radio was removed. My aftermarket radio was connected to the ground cable, but the other end wasn't even connected to the vehicle. You might want to ground your stereo chassis too, as well as making sure your ground cables on your radio are properly connected to a grounded source.
Next, you may need to get noise reduction units. I had no noise in my CD source, but I had awful noise in my AUX source. So, I ran a noise reducer through my AUX source plug, and that zapped it. You have to troubleshoot the system and determine what is causing the noise.
I actually purchased a noise reducer for my RCA cables, my power and my AUX. All three noise reducers cost me $25.00. I had this problem with stereo's in the past. In my Mustang, it was my power source that was causing the noise. In my Jeep, it was my AUX source. The problem is that when you amp the stereo, you also amp any noise interference.
Below the picture at the link to the power noise suppressor, there is a discount for all three noise supressors. There is a RCA noise suppressor, A line noise suppressor, and the power noise suppressor. I just brought all three for the discount, and I was able to troubleshoot exactly what source was causing my noise interference. It was the line noise suppressor that worked for me, which I connected to my AUX. I also threw in the power noise suppressor, into my system, just for good measure. The RCA noise suppressor did nothing for me, but I wasn't getting any noise from my CD source, so obviously it wasn't my amp or RCA's. Because, if it was, I would have been getting noise from all sources. I would also check to see if you get more noise from one source over another source.
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