We use several Bug-O products (Uni-Bugs, Stitch welder) but not the Speed Weaver, so I can't tell you much about them. I do have a suggestion, that you check to be sure your welding power supply is grounded. I don't mean the welding ground lead, I mean the power connection which connects the weld machine frame to an earth ground. If your grounding isn't connected right it might be that a small voltage is feeding back into your Bug-O and going to ground that way.
Also you might check the supply voltage to the Bug-O, make sure it's where it should be. Low voltage can cause motors to overheat.
If that doesn't work, since you sent it back to Bug-O and they say there's nothing wrong, I'd try to get a sales rep in your plant to see it for themselves.
I hope this helps.
CHGuilford