Suggestion
Its probably your source unit...or something in between it. Are you running a aftermarket deck? Do you have a EQ or some factory processor running between the amp and the deck? If you have a aftermarket deck...with sub pre-outs...make sure theyre not touching the chassis or any metal in the back of the deck. If you have a EQ...try it without the EQ...Ive ran into this problem with a couple of cars...once in my SC...on a newer Alpine (CDA-7873 I think) come to find out...my RCAs behind the deck were touching the mounting chassis...ended up grounding them out and sending it in for repair...other car was a 90 eclipse...running a aftermarket deck to the stock in-dash eq...removed the EQ and everything was fine...just remember...less is better...the more you add...the more noise your going to get...try to stay away from the cheaper brands.
My old setup (click here)
My Current Setup: (like anyone cares....)
HU: Clarion Drx9575rz
DSP: Clarion DPH7500
Fontstage: 5 1/4" Nakamichi seperates (soon to be HCCA 5s, got em...too lazy to install)
Rearfill: Soundstream B52 coaxilles
Sub: 1 Adire Audio Shiva in a 2.1 cu ft sealed enclosure
High/Mid amp: Alpine v12 4ch (maybe switching to my Nakamichi Pa304...laziness factor again)
Sub amp: JBL BP1200.1 running 600 watts at 4 ohms
Power: Lightning Audio 1 Farad Strike cap....and a Energizer Battery
Sean McL