Which system do you have? If you have the monsoon theres an amp that probably isn't turning off w/ your new radio installed. Put your head reaaaaally close to the speakers in the doors when it's completely still and silent, then listen for some static, or any sort of noise.
If that's the case you just need to bypass the amp. Unplug the amp, and jump from the input signal wires to the output signal wires on the connector to bypass it.
That's what the deal was with my Buick at least.
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