Well, that's the other end of the spectrum (and other end of the transmission, of course) but I can't say definitely not, either.
Stranger things have happened.
I think the key to this mystery is what I was doing to the car when this occurred.
I pulled away easy from a stop sign, then tromped on it once underway. A fast grab of 2nd, dropped the clutch pretty hard and laid down two black strips, then heard the noise as I eased back off the throttle.
It's been there ever since, even though the car drives just fine.
I get it up over 50 and the "switch" gets flipped and the racket begins, every time.