song quality

A lot of my down loads lately have been "reversed" in sound quality. Old songs (60s) and current songs (Billboard top 10)
The back ground vocals and rhythm guitar are "in front" and the lead vocals and lead guitar are buried in the back.
I thought it might be my computer getting hot, but I can listen to an archive song right aferwards and it sounds fine.
Is it me? Is it the down load? Is it my sound card/speakers? I am at a wits end.
Also.
Are they encoding songs now?
Tommy Lee's and Nelly's new ones will not down load....
thank you