Had both belts on my 2004 changed. Now squealing at start up.

OK that has a serpentine belt with an auto tensioner. You have an extra load somewhere causing the belt to slip. It could be a bad battery causing the alternator to work harder or it could be a power steering pump going bad causing the same thing. It could also be a worn bearing in one of the idler pulleys or the tensioner its self could be worn out. Here are a few ways to check and eliminate a few of these things. Next time you drive the car and it squeals make a note if you are driving straight or turning a corner. If its straight then we can pretty much rule out the power steering. After that we will look at the alternator. When you are driving and it starts to squeal turn off anything that uses electricity. i.e. heater blower rear defrost, headlights if its safe. If the squealing stops then you need to get your charging system checked.

After they changed the belts the 2nd time my water pump went bad. Changed that and the timing belt. At times I can actually hear both belts squealing,(it has two) one has a higher pitch than the other, I have noticed it squeal sometimes when I turn a corner (power steering) and the other belt (AC?) almost always when loaded. Why did the old belts not squeal but the new ones do? I am thinking you are right- maybe the tensioner or bearings in the idler pulley. At 144k though, I have had very little trouble. I just want it to quiet down! Thanks!

That's just a via Rio for ya dude... I have one, it all depends on the humidity, temperature, your habits if its a stick, lots of factors.