Engine sound threw speakers

hey guy's.

Ever since i bought the 20vt 3 weeks ago i've not been able to listen to any music and as the titel shows you might have guessed why that is.
here's the setup. Pioneer radio/cd players hoocked up to a amp in the boot. amp connected to the 4 speakers in the car. pretty basic. no subwoofer (yet if ill ever get one is the question). From the first drive i took it home there was the engine squeel in the speakers when the radio was playing. I know this can be many thing but ill list what i checked and what i've done and hopefully someone will guide me in the right direction to fixing this.
I found that the powercable for the amp and aux kabel( this how its called in englisch? the kabel going from the radio to the amp) where next to one a other pulled along the middle handbrake consol straight into the boot, this along with the 2 front speaker cables.
I removed the power cable from the middle and put it under the carpet on the right side where it come's into the car next to the seat, under the reat seat and into the boot.
aux, and 2 front speaker kables are still running threw the middle handbreak consol underneath the backseats and into the boot but now opposite of the powercable.
So in my boot you've got my power and my mass kabel comming from the lefthand side and the aux and all 4 speaker kabels comming from the right side.
Everything's properly connected to the amp like it should.
even remade my mass cause it was put together with a other mass and thought that might have been the problem. now its sitting on its own directly on the frame with no paint between the 2.
Still the same engine sound in the speakers. also when i turn the radio on or off when the engine is on i get a popping sound in the speakers.
anyone any idea what i've missed or done wrong or can improve?
thanks alot.

It could be many things, start by looking at where you have the system earthed/grounded.

Amp is grounded in the boot on the sparewheel bracket.

Try grounding the amp to the same point that the head unit is grounded or vice versa. Maybe this intro will give you some pointers further pointers:

http://www.crutchfield.com/S-wnmXf2x731z/learn/reviews/20030805/amplifier_noise.html

Go to the back of your stereo and ground the outer of the phono cable. If your ground has ever come off your amp the first thing it will do is try and draw current down the phono cable and burns the track out in the stereo let me know if it works

thanks for the advice, ill have a look.