Are you connected by chance in both locations to a cheap, non-filtered automotive battery charger? Many of the big booster/jump start chargers will havde a step down transforner and a rectifier, but no filtering, and many stereos will be suspect to the noise on the power supply wiring.
It is just a thought, since it is one possible situation that would create the noise you describe.
Proceed ONE STEP AT A TIME with the testing procedure David outlines above. Take your time and be patient. With a systematic approach, the offendig noise will make itself apparent.