I have a cd3200 (eclipse) head unit with 5 volt preouts and a fosgate T400-4. When I position the gain above 2 there is a slight sound emitting from the front speakers that worsens as I add gain. The front 2 channels of this amp power 2 focal 165v1's and the rear channels are bridged to run a 10 inch jl sub. The focals do not emit this sound when the sub-pre out is disconnected. An installer suggested regrounding which was done and we are convinced this is not the issue (the pitch does not change engine rpm and is only present when the sub/pre out is connected)