Low rumble/Distortion from factory radio...HELP!

[blakeduren]

83 factory tape player head unit
I replaced the front and rear speakers with 3.5s and 4x10, just basic replacements months ago....everything was great.

A few days ago I noticed a strong low rumble/distortion from all of the speakers at all times(am/fm/tape). The pitch of the distortion changes slightly with the RPM of the engine.

Any thoughts?
I will say that I recently replaced the windshield(radio reception is still good), and replaced all the in-dash bulbs...did I mess up a wire while I was back there?

Thanks,
Blake