Yeah, as they say, these things run on smoke and if you let it out, they won't run. If it's coming from under the sink, I think it's probably one or more of the FETs. That stuttering is called cogging and if you stay on the throttle while it does this it flows LOTS of current through the esc and things get very hot very quickly. My best guesses on the cogging are either a bad connection someplace, overgearing, driveline hangup, or sub standard batteries.

These are just guesses of course, but generally speaking, smoke is a bad thing.