Hello.

I'm a newbie on car audio. I've never installed a sinlgle headunit, amp nor speaker in car. Yet I've red much about these things and understand some in.

I had my car setup made in a store ~2 years ago. They installed the empeg, a ~40W RMS amp under the right seat and 6x9s on the back.

Installers did a crappy job, right after the car was ready to be picked up there was a high pitch noise coming from the rear speakers, newbie as I was I got fooled.

Well, to the point. I hear this noise every now and then. Comes randomly. I've noticed that cold weather and bumps affect on it.

How to remove the noise? What to check?
I don't have access to a pair of car-speakers nor another amplifier. And since the noise comes in randomly, debugging is a bit hard for me.

I can remove the noise by removing the empeg from the sled. Powering off the empeg won't do the thing.

Dunno if you understood my point, sorry for the incomprehensible english on audio terms d=D

Well, to the point. I hear this noise every now and then. Comes randomly. I've noticed that cold weather and bumps affect on it.

That sounds like a wiring fault somewhere. A loose connection, or a bare section of wire rubbing against some metal in the car.

Check this, read this, and then go through the troubleshooting steps here.