I had Best buy install my amp thinking that they could do a better job thenI could.I guessI was wrong. WheneverI turn on my car my sub makes a huge thump, even with the radio off. Then it hums when im driving, again, with the radio off.I think its a ground problem.I checked back there and it looked fine but there is a line out converter (which he shouldn't have had to use) that has the 2 rca cabes coming from the converter, and a black wire coming from the middle of the two. I'm pretty shure the back wire should be grounded, but its not. Anybody no for shure?Should I ground the black wire?

 

It sounds like they wired the control lead of the amp directly to the ignition rather than the amp circuit lead off the back of the stereo head unit in the dash. The amp should be off when the radio is off. I'd take it back and have them correct that mistake. It never hurts to double check ground wires, but I think you are hearing speaker feedback from the amp when the radio is off (which is one reason why the amp is usually turned off with the radio).

I would not assume it is a ground lead without looking at a schematic (documentation should have come with the parts) or at least testing for voltage while the system is on. I tried to look this device up on the Best Buy site, but couldn't find it. If it isn't hooked up to anything, I agree, it can likely be removed from the system.