okay, i went out and got a decent HU this time, a Pioneer 3900, within a month i took it back, i was getting "feedback" from my subs, sounded like something was grounding. before i took it back, i ran another set of RCA's with a line converter to the rear speakers (the subs were on a sub channel first), no problems, sounded great. i didn't keep that for long because i lost the ability to tune my subs easily, which matters because i often listen to music direct from the studio that hasn't been mixed (high bass levels). so, took it back, upgraded it to the 4900... why?...i don't know! about 3 weeks later, that familiar sound seemed to be peeking its head out again. so here i am 6 weeks after install, can't take i t back to the store, and Pioneer wont replace it, just repair it, which might cost me....i was so f!@#$@% ****ed, and i know some people are gonna hate this next statement, but i really wished i would have kept my Sony!
Typically output converters use transformer coupling which completely isolates the radio from the amp. Whats happening in your Pioneer is a common problem. But its caused by the amp. Whats happening is the device that Pioneer uses to float the signal ground above chassis ground (we do this to prevent noise) has become shorted. The chassis ground and the signal ground are now the same (bad very bad). Something in the amp has caused current to return to the radio via the RCA shield. First double check the amp, make sure the ground is solid. And I don't mean tug lightly with tweesers. The Pioneer radio can be fixed, but instead of replacing the device, replace it with a chassis 000 resistor. They are really cheap. I might be able to show you the part that needs to be replaced. Take the top of the radio off, remove the CD mech (4 screws and unplug one ribbon cable) Take a clear close up picture of the circuit board. Especially around the RCA area. Post the picture. I have not seen this problem with the 3900 or the 4900, but I have seen this alot with models from the last two years. I am assuming its still the same problem.
