I finished installing a sony xm-7557 and I'm hearing a slight hum form the alternater. The power wire coming in is 4 guage split into two 8 guage for the different power supplys. The ground (until I get more 4 guage wire) is a single 8 guage. I'm pretty sure the problem is the ground but a friend told me the whine could be from the amps chasis being screwed to the car's chasis.
Is this true?

Thanks

 

make am amp rack, and find out. it sounds possible. amps werent designed to be grounded by the body of the amp.

adam

 

Sony.

Check your gounds.

But it's a high possibility that it's just your amp....

 

Sony amps aren't known for their quality, but they should at least be good enough not to have whine.

Yes, mounting the amps directly to metal can create a ground loop which results in alternator whine. This is why a lot of amps come with plastic inserts that the mounting screws go through. The case of the amp is grounded, so if you attach it to the chassis, you wind up with 2 ground paths which can cause a ground loop, especially considering that in most cases you're just screwing into sheet metal which doesn't make the best ground.

Also... if your amps are screwed to the floor above the gas tank, I would HIGHLY reccomend you find a new way to mount them. In the event of a rear-end collision, do you want a bunch of screws 1/4" above the gas tank?