Do you have the front/rear antenna? ie one in the windshield and another (Fuba?)
up on the roof? According to the Bentley for my '91 200 the front antenna is FM
only while the rear is AM/FM. If you just changed radios you may have plugged
in the wrong antenna. My factory radio had inputs for both front/rear antennae.
I also had poor reception until I checked the antenna connections on the roof.
The cable had actually worked itself loose. There may also be a wire that
supplies power to the Fuba antenna on the roof, it's amplified.
I just installed a Blaupunkt head unit and CD changer and am also getting a
"pop" when I power up. Mine is fairly quiet though, I think it's due to a
grounding problem/differential between the amp and the rest of the system.
There are several audio gurus out there, including some guys who built and
competed in the car stereo competitions. If you have an answer to the "popping"
question could you forward it to me?