[mikegett]

LOC's are bad for ground loops. It could be a poor LOC or it could be your ground location. A ground loop is formed when two electrical devices are grounded to the same piece of metal but at different locations. It creates a EM field that emits electrical noise like your rpm's and Air conditioning. Some LOC's have a built in ground. Others have a ground line. A older sosche LOC I had used the built in ground. It seemed to be the best for getting rid of the ground loops. If your LOC has a seperate ground, you should first place it at the same location your amp grounds. The bolt you mentioned is a decent spot. If you still have engine noise, try unplugging the factory amp. It may be grounded at a similar location and causing the noise. If you still have the noise, then run a quick test line directly to the battery ground. If you still have the noise the LOC is probably bad.