The symptoms you describe, crackling and popping of speakers is characteristic of a bad BOSE amp. After having the problem you descrived, I had to have my Bose AMP replaced. My unit however is the older 7 channel Bose amp. The MB Radio has the Becker unit installed in the front dash and the tuner in the trunk.
If you radio is a Becker unit, you can call their US location and speak with a tech rep for further help.
You will not get any help from Bose.