I had a 2000 323i and the rear when I turned on the rear defrost it did the same thing to my radio. Someone had told me that BMW had a fix for it, but I never went and had it checked since it was out of warranty, and I pretty much never use the rear defrost in Florida.
As far as the fan problem, Im not sure what the "noise" your hearing is but the fan will change speeds depending on the engine temp. I had problems with the fan in that car also, I was just getting ready to change that fan out when the subframe tore loose from the chassis, so I never had a chance. Good luck with it though.
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