alpine am radio howl / warble - not alternator/ignition

[jfc68]

looking for help with an AM reception issue

I have 2003 silverado w/ alpine h/u and 2 fosgate amps under back seat

FM reception is fine - so is CD - all clear sound with motor off or on

however, AM is very bad with feedback / howl / warble that rises and falls

it does this with the motor on or off

I have checked most of the grounds etc and the antenna - tried removing the whip etc.

I also disconnected the 100amp fuse to the amps and the sound is still there from the fronts...

I am considering

- checking with a separate battery?

- testing for any and all ground loops?

- I tried removing many of the fuses one at a time to see if it stops - no luck

also, and this may be a contributing factor...

when I use the power windows on the passenger side, there is a loud raspy noise

in the system - BUT not when the dirver's side power ones are used....

any sugguestions?

please help

thank you,

john

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