4T60E Noise downshifting into 3rd.

1996 Riviera. 198,000 miles.
Yesterday as I was driving at approximately 50 mph and gently accelerated, the transmission made a screeching/grinding noise as it came out of overdrive into 3rd. :eek: "What the hell was that!?"

I can also feel it to some extent.

I've been able to repeat it several times, but noticed this morning on the way to work it was less severe.

Possible the TCC solenoid is sticking? Or symptom of a bigger problem like the torque converter going bad.

Other than this noise it is quiet and shifts fine. Fluid was changed when I bought the car and went over everything about 5,000 miles ago.

Thanks in advance.