ok here's my 2 cents / i think some of it has to do with mp3 or wav editing software, mainly normalizing process. if it is normalized once or twice you probably can't tell the difference in sound quality but every time you do it, it adds up after exchanging hands many times with users (like me) that prefer to edit their mp3's.....
but i think most of the damage comes from multi-tasking or like playing quake or some other 3d shooter game while upload or especially downloading mp3's (das where them bleeps get in). unless everybody had alot of computer hardware horse-power we are probably gonna always have them bleeps.....