some people asked about it already, but in my case it isn't a problem with the CD drive (it happens even when I take it out). I run procmon from SysInternals for a while and found out, that svchost.exe makes some registry calls to following keys:
I did a fresh Windows 7 Pro 64bit installation few days ago, because my old HDD died. The new HDD is a 1TB 2,5" HDD from Samsung. The laptop is a Thinkpad T400 2767-B44 with 8GB RAM. I never had this strange behaviour until now.
Thank you for the help!