Paul,

What amp(s) did you end up with?

I'd seriously question the assertion that it's entirely down to the alternator. The Imprezza's certainly not a problem car in terms of interference - Japanese cars in general tend to be pretty well supressed and very rarely give us any problems. As for disconnecting the alternator plug to see if the noise goes away, all I can say is, don't do it! The chances of blowing the rectifier diodes in the alternator are quite good, to say the very least......

I've done another Empeg install again this afternoon, on a Rover 620, and initially had some noise on the system. In the end, I managed to cut it down to the point where it was no longer an issue. To give you some ideas, what I did in the end was:-

Move the Empeg's power filter a good 12" away from *all* the Empegs other cabling.
Run a very heavy earth cable from the Empeg ground connector down to the amp earth.
Install a 1uf cap onto the alternator output.

That cut the noise to the point where you had to have the headlights on full beam, the heated rear screen on, the Empeg on full volume, and playback paused to even hear a trace of noise. Moving the Empeg RCA ground leads from the main amp earth to another point in the vehicle then cut the noise further, and disconnecting them entirely completely eliminated it. Having spoken to Hugo on a good few occasions about these, I decided not to leave them disconnected, and instead gave the customer an easy means by which to remove them at leisure if he wished.

The Subaru, if anything, should be even less prone to noise than the Rover, although thanks to Honda's influence, they're pretty similar cars electrically. Personally, I'd go back and give the fitter a hard time (we love it really ;-) Yes, the alternator might be the source of the problem, but it's *their* job to find a way around it.

If you don't have any joy, and can't get the noise to a point where you can live with it, let me know, and I'll see if I can come up with a solution.
Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk