Thanks for all the help everyone. I tried everything you suggested without luck. However, the problem is now solved. Long story short: It was a bad spindle. Inventables sent me a replacement and everything is working perfectly again. I was using the 24V Quiet Cut spindle that came with my X-Carve kit last year.
The long story:
I eventually noticed that the stepper motors where chugging (for lack of a better word) slightly while carving. It was hard to hear but they didn’t sound like they were running smoothly. I decided to turn off the spindle and run a test carve in the air. The steppers hummed along smoothly–no chugging. When I turned the spindle on during the carve, I heard the chugging again. So apparently this is the result of noise from a failing 24V Quiet Cut spindle interfering with the steppers. I dropped in the new spindle and everything is dandy–actually it’s carving better than ever thanks to all the fine tuning I did while troubleshooting.
I appreciate the help and thanks to Inventables for sending me a replacement spindle. Time for a DeWalt 611…