2006 Yamaha 250F belt squeal

I am new to this site, so I am praying I am doingthis right. I have a 250F Four Stroke and after it runs for about an hour when I back it down to idle I hear a squealing until I get back on the gas then it stop. Doesn't happen often. If anyone can get me a starting place would be great.

[boats.net]

Could be the idler pulley. It may still have warranty left on it.

Thank you for the info!

Its the driveshaft. There are two guide bushings. One just above the water pump housing, and one near the top, under the oil pump. The bushing is self lubricated with water. Take the gearcase off, and apply molybendum grease to the smooth raised sections of the driveshaft. Once every other year when you do a water pump and its good to go.

Thank you again, this information was helpful.