car radio filter/alternator noise?

[gery350]

hey guys,
just installed a system in my car(amp,woofers,etc).
the new radio i installed is sending alternator noise to the amp.
i assume i will be needing a filter for the (+) of the radio to eliminate the noise.
i installed a system on my sons car as well and did not get the noise.
my question is do some radios come with built in filters or is there another reason why i am getting the noise.
thanks in advance, gery

[yfz122]

Check your grounds. Are your audio and power wires ran separately?

[novadave]

Try running a source ground(16 ga. wire from head unit to amp).

[IXIswamperIXI]

Make sure that the amplifiers have a good ground first. Use at least 10 Gauge wires for the grounds (and power). If you have 2 or more amplifiers, DO NOT go from the ground terminal of one amp to the other and then from there to ground, most likely you will have noise. Ground each amplifier independently.