Sound Quality

[#1]

Sinse I have had Windows 7 I have found that some of my cds have bad sound qualities but most of them are ok I have cleaned these CDs but it makes no difference.

[#2]

DRM    on the cd? Does it play fine in a normal cd player?

[#3]

Not likely to be DRM.  Could be faulty hardware but most likely to be a corrupted sound driver or even just odd settings.
Check the properties of your driver and see if the settings are what you would want them to be. 
After that try getting a new driver for your soundcard/sound chip on your mobo.  I would always uninstall/reboot/install drivers.
Good luck.

[#4]

I would say a bad driver IF it was all cd's but just some
Most OS's these days use digital extraction from the cd which is why I suggest DRM, esp. if the cd is a SONY release.

[#5]

What are you usu]ing to play the CDs.
I suggest trying in various players like WinAmp, VLC player, etc to see if you still get the same problem.