Delta SCMS vibration problem

I have a Delta 36-250 SCMS and I'm wondering if anybody else has had this problem:
When I pull the trigger to start the saw, the blade jumps to life and starts to spin just like you'd expect, but for the first second or so (sometimes longer, maybe two seconds) there's a loud buzzing noise. The buzzing sound is distinctly different from the "normal" sound of the universal motor winding up. After watching this carefully for a number of starts, I noticed that the blade vibrates while the motor is buzzing, and stops vibrating (visibly, anyway) when the buzzing stops.
To further complicate things, the problem doesn't appear to be startup-related only. I've had it vibrate/buzz in the middle of a cut when the saw is under load, although not overloaded, and you can imagine what this does for accuracy when cutting maple face-frame parts...
The blade I usually use on this saw is a Freud 60T Negative-hook SCMS blade, and it's sharp and reasonably clean. I've since tried a Freud 80T thin-kerf crosscut blade, and I think any difference it made was purely psychological. Arbor bolt, washer and flange are clean. There does not appear to be any noticeable side-to-side movement in the arbor, but there appears to be a small amount of backlash in the gearbox, which I would expect as normal. Other than the extra blade marks when the blade is vibrating (which is maybe a third of the cut) the cuts are clean, smooth and unburned.
Returning or exchanging the saw isn't an option, as it's several years old. It's seen very little use, probably not even an hour total run time, as I've not had much time for woodworking in the last few years. As far as I can tell, it's done this since new and it's taken me a while to figure that the problems weren't related to me deflecting the blade while cutting.
Has anybody here had a similar experience, or any ideas as to what it might be before I dig out the wrenches and screwdrivers and go prospecting?
Greg
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I have notice the same thing & have done the same check list.. I am convinced that it is in fact the Drive Grears "worm??" and have decided to let her go until it blows,, it does not affect the Cuts..

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