Mate,
I have a guarateed cure for you. It is a bit old school but it works.
Here is what you do:
- Get a large steel shacle. About 2 - 3 inches.
- Then get about 8 or so metres of 16 guage insulated cable.
- Start threading the cable tightly though the centre of the shackle and wind it tightly through and around, throggh and around, the entire circumference of the shackle. The idea is to imaginne the shackle as a circle and you are covering the circle in several windings (or turns) or wire.
- Connect this wire in series with the 12 volt input of your amp. (add a fuse if you like).
- Start engine, turn on amp, and listen to whine-free clear sound.
If you have a massive sound system, which I suspect you do, you should use a higher current cable, and a proportionaly larger shackle. What you are doing is creating a large inductor to attenuate the whine.
I had EXACTLY the same problem in my R33. I made one, and installed it in the boot. Like I said, it is very old school, but, it works.
PM me if I have not described the process well enough, or you need more info.
regards, Steve.