installed a new amp other day and notice when the car is cold it makes a whine noise like a s/c it sounds like its coming from the front of my car but if i turn the sterio all the way down it disapears

what do you guys reckon

iv herd if the amps not earthed properly it can do this

Sounds like a bad ground. Did you sand the ground back to bare metal?
Also running the rca's along side the power wire can cause this.
Also if the headunit has blown an interal ground track the same noise will occour.
So try re grounding your amp.
Moving your rca's if they are running next to the power wire.
And if that dosnt work try grounding your rca's at the headunit.
The screw holes on the side of the cd player are perfect for this. Screw a wire in there and Run it from there and wrap it around the rca's at the back of the headunit.
Good luck.

Also another note, if your ground wire is smaller then your power wire it could cause interferance.

ahh that could be it i also have my subs huge a** power cable next to the rca's so yeah il try changing that but first to ground it properly

thanks for the good advise

No worries mate. Good luck with it.
Let us know how you go.