Hi, all!

I bought a 1991 740 SE Turbo Wagon a few days ago (I love this car!)
Had to leave the radio on for my daily drive in order to reset it to "cod e" mode (someone tried wrong code and it was showing "EEE").

I believe the radio is currently in AM mode (as in AM/FM)

I noticed a few types of static coming from (mainly) the rear right speaker:
- When driving: static from rear right speaker which changes with engine rpm (interference from spark plugs?) and when
- when operating right power windows -- very loud static (as if the electric motor's operation is being put through the speaker). Left windows: no or almost no noise.
- when the engine is off, key still in, I am not touching any controls: strange, "in between stations" noise which dies if I open the door or turn the dome light on (radio is still on)

Both noises are not affected by the volume control (I presume because radio is locked).

I will retrieve my code from a dealer today, but the noise is really bothering me. I am considering changing the stock casette stereo with a cd/mp3 player (Blaupunkt mp3000 was recommended to me by a friend, $125 on ebay) but am concerned that the noise will remain.

Any suggestions / experience?

If I come to a solution, I will make sure to share it here.
Thank you in advance!