I have a bunch of old hard drive platters. They make great toolbox mirrors, won't break, and a few scratches don't really matter. I've even got a platter from a laptop drive in my wallet that I've used as a mirror a few times. :)

I'd be curious if a flash based mp3 player would cause the same problems. I could see that the microdrive might cause more interference due to the magnets and moving parts/fields in the microdrive. On the other hand, could it be caused by the decoding chip itself?