crunchy drivetrain question

Hi everyone (except for the spammers)!

I just replaced my chain, cassette and rear derailleur on my bike. I
adjusted the H and L screws, the B screw and the indexing. It works
great on the stand or just spinning along. When I apply a little
power, it sounds 'crunchy' at the bottom of the derailleur when the
chain passes near the lower pulley. I also checked the chain for stiff
links and found none. The derailleur lines up perfectly with the cogs
it seems, and the alignment of the RD hanger looks straight to
me...it's an 8 speed drivetrain with old Ultegra 600 brifters up front
and an SRAM cassette out back with a Deore longcage RD...What am I
missing here?