Car amplifier noise - help!

[Seraphim]

I've just stuffed an amp in the boot of my car to power the front speakers - I've just this afternoon got everything wired up, and there's noise, and lot's of it!

I get a constant buzzing (with engine off) which is then joined by the typical alternator whine I've heard before when the engine is running. Has anyone got any tips on how I can troubleshoot this problem? I've got the amp grounded to the body at an existing ground point which is shared with something else - maybe the rear cluster... Is this a bad idea? Should the amp have it's own dedicated ground?

I've Googled for all I'm worth and I think I'm more confused than ever. Any help (and I mean any) will be exceptionally greatfully received. It's driving me insane!

 

[Seraphim]

A dodgy ground might be a culprit. Is there a good connection to unpainted metal. It want's to be as near as poss to the amp.
I sanded the body at the grounding point, so it's a pretty good connection. I could try sanding it more - there's still a little paint on it... Amp is grounded via a 50cm wire of the same gauge as the positive.

Got good solid connection to the battery? Well, every connection needs to be good really.
As far as I can tell, it's all solid - short length of 4AWG to a two-output fuse distribution block (for an eventual second amp) with 8AWG running to the amp

Have you got the power cable running next to your speaker/RCA leads? Are the RCA leads shielded?
Power is running down the opposite side to the audio - and using shielded and unshielded cables doesn't seem to make a difference.

It could also be worth checking the wiring under the bonnet - alternator to battery, battery to chassis earth, etc.

Head unit earth might need a proper connection straight to the chassis. It might be dodgy.

Try testing the amp and wiring using a different source - mp3 player, cd player etc. both at the amp end and the HU end. That might show up where the problem lies.
I certainly will try the amp with different sources tomorrow, and grounding the head unit to the chassis.

Ta for the help, you've given me a few ideas of things to try!

 

[Seraphim]

Ah, top idea Mickey, I'll give that one a go in the morning. It's times like this I wish I had a garage I could work in. Damn these short days!