I also have the problem, the crossfading option fixes it, but also reducing the volume (in rythmbox!) did.
Ubuntu Gutsy IBM/Lenovo Thinkpad Z60m 00:1b.0 Audio device: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) High Definition Audio Controller (rev 03)
I also have the problem, the crossfading option fixes it, but also reducing the volume (in rythmbox!) did.
Ubuntu Gutsy FBM/FR/ FW/FRW (ICH6 Family) High Definition Audio Controller (rev 03)
IBM/Lenovo Thinkpad Z60m
00:1b.0 Audio device: Intel Corporation 82801FB/