I have about 2500-3000 on my drivetrain and last week noticed a 'grindy' feeling when pedaling before a crit. I lubed the chain and the other moving parts as best as I could and the feeling (there was no sound of grinding/abrasion anywhere) didn't go away. Starting thinking it was the chain and went to LBS and they confirmed. Bought and installed new chain, but feeling is still there. When I turn the cranks very slowly it's like there's a repeated catch and release, if that makes any sense. it happens when turning the cranks both forward and backward. I didn't notice it when i turned the cranks with the chain off so i don't think it's a BB, likewise I didn't notice anything weird with the cassette with the chain off. and the wheel spins ok so I don't think it's a hub issue. I rode the new chain and there wasn't any slippage on the cassette or the chainrings even when shifting under stress, and there wasn't any issue with the shifting so I don't think it's a deraileur adjustment.i'm starting to wonder about the RD pulleys - those were the only things i didn't really check, although i did clean them and the seemed to spin all right - plus this 'catch/release' seems too significant to be coming from those two little guys.
any ideas?

A new chain behaving poorly on a worn cassette is telling you that the cassette needs replacement as well.

A bad or sticky link in the chain ? Slowly pedal backwards and watch the chain as it goes over the jockey wheel or pulley to see if it skips a bit.

a BB without the chain has no load on it and may not show any symptoms. i wouldn't necessarily count it out as a "person of interest".