Audio Systems: NOISE, noise loop, noise eliminator

Question
im getting a motor noise out fo the speakers
i have a 5 chanel amp and don't know if it is a noise loop on the speaker wires or the amp.
I have a 20-amp filter on the radio and 4g.wire on the amp + and - is there a way to filter the power supply to the amp?
if i turn up the gain on the amp noise is incresed.
or should i look at the ground conections ?

Answer
Rich,

go to the grounds first , make sure they are under 3 feet away from the amp and heavy gauge, mounted tight to bare metal piece of the body...also just go over all your wires making sure there is no damage and that all connections are secure, also clean your battery terminals and main terminal wire leds, along with your direct feeds to your amp... now after all of this check for the noise , if you still have it i would recommend stopping by radio shack and just picking up a distortion blocker/noise eliminator, i'm unfamiler with the filter you are currently using so you can try the new box with and then without your current filter to note the difference... hope this helps you out if you need anything else just let me know

thanks