My hummer has begun to produce a squeeling noise when I am driving. I understand its hard to diagnos a nois, but it sounds like its from the engine. Has anyone had a similar issue?

I have never experienced this sort of noise before. However, I would expect that the list of potential causes from least to worst serious (and expensive) would include the following. Your serpentine belt is loose or cracked and needs to be tensioned or replaced. Your alternator, AC compressor, water pump, or one of the other devices run by the belt has developed a bearing problem and needs replacement. Finally, you may be developing a problem with the engine drive shaft bearings (Hopefully not). You should take it in to a mechanic as soon as possible.

If its a squealing noise you hear coming from the center of the engine while driving it is unfortunately your water pump my friend....Hummers with the GM 3.7Liter 5 cylinder are notorious for having faulty radiators and water pumps. The bearing on your water pump is most likely bad and is leaking coolant onto your belt..hence the squealing. repairs for this will range but expect to pay around 650. I would change out the thermostat housing at the same time. ( another 250 in parts/labor) but worth it.....Also have the mechanic change the welds on the sides of the radiator they leak usually around the 70k mileage mark. Pumps are leaking around the 90k mark