Thread: Sudden alt. noise from phillips SndCard

Upgraded to phillips soundcard that works great on my home computer so I got another for my truck. I had the thing working sterio from the on-board sound, but liked the 3d effect the phillips card offered. The computer gets absolutely no outside noise, distortion from running the front two speakers off the amp. However, as soon I connect the rear speakers, even if by themslves without the front channel's in, I get alt. whine. Anyone encountered this? I don't get any ground loops from the sterio, but rear speakers cause trouble.. why? going to try in-line ground loop filters, but they cost 35 bucks a piece.