2005 Equinox buzzing in all speakers.
 

My Equinox has a low buzzing sound in all speakers that increases in intensity when the motor is revved. The only times it doesn't buzz is when the car is turned off or when the amp under the back seat is unplugged. Radio on or off doesn't make a difference. I have noticed that all of the speakers on the driver's side of the car sound muffled when tuning the fade and balance. It sounds like the amp may be bad. Is there a way to put an aftermarket stereo in and bypass the amp altogether? I'm not too concerned with keeping the current radio because it has the "CD changer error" error too.

I downloaded the wiring diagram from a similar post and looped the speaker wires in the plug from the amp. I happened to have a GM wire harness from something that had the right number of wires. I just jumped them over to see if it would work. It sounds better than ever. Apparently the amp is bad. When I unplugged the connector that supplies the power and runs the subwoofer, it was all sticky as shown in the pic below. I guess the previous owner dumped a sod or something on it. Under the back seat is a bad location for the amp if you have kids. All speakers work great except the sub, which is only powered from the amp, not the radio. I put some duct tape on it to keep it stable. If it becomes a problem, I will splice the wires but it looks like it would be a pain since there isn't much length to them. The last pic is of the grimy power plug.

Wiring harness
 

Anyway you can post color to pins for me I can see the top one fine just not the bottow.

Amp
 

I installed an amp on my 2008 Nox when new. Took it to several stereo places with est. $600-1800. Called Crutchfield and got 350A and new speakers for $450 with inst. instructions. Sounds great!!! Used stock radio because w/amarket radios need different wire harness which is $$$$$. Also lucky if everything works after changing harness because many things run thru radio. Installed amp under rear seat with no problems so far! Where else could it go? Sounds better than weak stock radio and better than optional Pioneer system offered at premium price.;););););)