Problem solved
For kicks and giggles, I decided to disassemble and check the other spindle, shaft, internal collar, and bearings even though I had no previous indication of an issue. The spindle assembly was fine, the shaft and collar had spot rust from hosing the deck down over the 13 years of use, and the bearings seemed slightly dry and worn. Being that I had a set of bearings from the parts shop, I decided to replace the non blade brake side. I cleaned the spindle assembly, shaft, collar, packed housing with grease, and pressed in the two new bearings. Reassembled both sides and held my breath as I started the mower and engaged the blades. Nothing but engine sound -- FIXED, no more spindle whine

. Two lessons learned: 1. If you need to replace bearings, spend a little extra $$ and do them on all spindles, 2. Keep your bearings greased! Final note - my neighbor has the same mower, just a year older. The spindles have grease fittings and he has not had bearing issues. I speculate that Troybilt did away with the grease fittings to save $$ beginning with my model year.