A few thoughts,
Have you opened the hood and to check the oil level and verify the air cleaner was installed correctly? This especially applies for chain shop and quick lube places.
How old is the battery, the alternator on my 2000 Blazer starts whining when it's overworked trying to recharge a weak battery. The battery voltage should range from 11.9V (fully discharged) to 12.6V (100% charged). I've noticed a partially discharged battery (~12.1V 25% charged) causes driveability problems with the Blazer. Most parts stores (Autozone, Advance, etc) will check the battery for free.
How worn is the serpentine belt? A worn out belt can cause all sorts of noises.