Mariopathfinder

Hello All,
Just took in my 2002 Pathfinder LE to my local dealer for an oil change and to check my belts which squeal terribly on startup after the truck has been sitting awhile. (i assume it is my belts) The dealership charged me $20 to tighten the belts since the warranty on them only lasted to 12000 miles and i was 600 over that. anyway, the belt still squealed the next morning. I washed it on sunday and as i was wiping down the engine compartment i noticed the main belt was very dirty, possibly greasy after the dealer told me they dont put dressing on the belts but instead tighten them and it is common with these belts which have a nylon core to squeal after 13-17000 miles. Took it in again and they kept it overnight, said they couldnt re-create the problem but tightened both belts and i was on my way. Sure enough, this morning the thing squealed like a stuck pig. anybody experiencing a similar problem out there with such low mileage?