Just got back from the dealer to have a squeaking belt idler pulley replaced. It was the idler pulley nearest the top of the engine, directly above the tensioner. It started squeaking two weeks ago, right after a "Simple Green" treatment to remove oil change residue (but never again -- I have the deflector now). I didn't really douse the engine with cleaner or use high pressure, but the squeak started the next day and within two days turned into a real screech.

Go to dealer. I suspect belt tensioner. Mechanic says, "Nope, it's this here idler pulley." They have to order part. Squeek/screech stops next day. Part comes in. Installed today. Under warantee, no charge. Kudos again to Fresno Lincoln Mercury -- not even a peep about the underdrive pulleys maybe being responsible.

Visual inspection of removed part shows nothing weird. Bearing doesn't feel loose inside the pulley either. They wouldn't let me take the old part home and tear it apart 'cuz they wanted to send it back to L/M.

BTW, the part number for the Dayco Poly Cog belt if you have u/d pulleys 5060923 (and right under that # it has in smaller print "6PK2345").

Just wanted to share the info.