[Starter986]

Got bored. Figured what could be the worst outcome. A couple of hours... maybe 1 hour without screwing around. I was in no hurry.

Removed the pulleys. Didn't have a 15mm (!!!!!) for the nut behind the tensioner pulley. 5/8 sufficed.

Completely dismantled (ha-ha) the three pulleys, keeping each one separate to not mix anything up.

Used brake cleaner and went to town. Completely clean. After removing the bearing seal-ring... zero lube. However, my examination revealed no play... nice smooth operation and rolling. I regreased all the bearings... and the contact parts. Blue loctite. Torqued.

Cleaned off the pulleys roller surface. Washed the belt in the sink. Installed belt. Buttoned back up everything.

Fired her up. Whirring gone 80%. Maybe 100%. I'm thinking the whirring got louder over time... maybe the whirring slightly was there when I bought the car, thinking it was an ordinary sound (nothing extraordinary), and progressively it got worse until it just overwhelmed all the other engine sounds.

I consider it a success... unless and until it resurfaces. Then I'll just get a new set of Mubea pulleys... for that is what is on it now.

For now the effort saved me, temporarily, ~$275 pulleys and belt.

Again, thank you for the recommendations.