belt noise / squeak

My 1999 Suburban has had an on-again off-again belt squeak / chirp for going on 2 years.
It is more pronounced in wet and humid weather, and goes away in hot, dry weather.
I've replaced the tensioner, the idler, the water pump, the belt, and the alternator over the last 6 months and it still sqeaks/chirps.
The only components on the belt drive that haven't been replaced are the power steering pump and the AC compressor.
It doesn't make a difference whether the AC is on or off.
It is starting to drive me crazy. Any suggestions are greatly appreciated.

Mine also gets noisy (although not a full on squeek) when the weather is wet. But than again, so does my volvo. Have you tried putting on some belt dressing? It's available at auto parts stores and helps quiet the belts. Also, check your belt tension to make sure it's within specs.