Another "find that whine" thread

[Philthy]

Hey, I have slight engine noise coming through the rear speakers only, that I set about fixing today, but have just hit a wall.

Things I have checked:
- All RCA connections, and proximity to high-current cables
- Different set of RCA's (run down the centre of the car straight to the amp, away from ALL cables)
- Swapped F/R RCAs over at headunit end so it is sending front signal to rears
- 2 new earth points (all sanded to bare metal)
- Swapped channels on the amp

After everything I tried, the noise is ALWAYS out the rear speakers, fronts are always fine. So correct me if I've missed something obvious, but as far as I can tell, its not the RCAs, headunit, earth, or the amp itself. It must be post-amp, but the noise is in each rear speaker equally, and both are wired direct to amp with good speaker wire.
The whine is only while the engine is running, and the pitch increases with engine revs

Fronts and rears are running of the same 4ch amp, speakers are Alpine type-s coaxials, headunit is a JVC-AVX2 (pretty sure thats the model, I'll check in a minute)

[Joe Bellissimo]

Does the whine still come through with the RCA cables removed?

[sweefu]

does it change as you rev the car mate?

[Philthy]

Changes in pitch when i rev the car, and no, there was no whine when RCAs were disconnected

[Joe Bellissimo]

Why don't you try moving the amp to a different location.

[Philthy]

Thats the 1 thing I didn't try. But does it explain the rears being the only ones whining no matter what signal they get or amp channel they are run off?

EDIT: Too quick to hit reply! I meant to add that the amp is under a false floor that I just put back in coz I need the car tonight, so testing most things that I haven't already done will have to wait a day or so