I'll be watching this thread - my Christmas present was a Brother SE-400. So far, it works great and I love it.
It's interesting that you can hear that the machine has a problem. Can you isolate where the choppiness is coming from? That might help with trouble shooting the problem.
Recently my resident handyman (DH) cleaned my HQ16 after 2 years of medium use. It was spotless except for a strand of thread caught in one of the gears. It hadn't caused problems before the cleaning, but removing it means that it won't cause problems after.
Mitch|'s Mom mentions something similar on her PC6500.
Good luck!