Little Update: I'm still confused!
On Thursday I went out to crank it before making a trip to the store. This was my first time driving it in 2 weeks. It had already been raining earlier that day & was lightly misting when I popped the hood. I noticed the pulleys & belt to be coated with moisture. The rain is obviously splattering inside the engine compartment, but I'm not sure what I can do to seal it off. I wiped things down as best as I could & started the engine. It didn't squeak immediately but started shortly afterward. It was just the occasional chirp that it does when at idle. I tried to check the tensioner by lightly placing pressure on it. It seemed to slightly change noise as I added tension, but I can't swear to it. I didn't have much time to investigate as the rain was beginning to pick up. I went ahead & drove to the store, & the chirps/squeals intensified as they had in the past. It did this on the way to the store & back home. I figured I could chalk it up to moisture being the main culprit, but I dunno.
Well, Friday I looked it over really good for leaks. I couldn't find coolant anywhere, even after letting the engine warm up. All pulleys look to be in correct alignment, & it's still running the old Gatorback belt. It never chirped after cranking/idling, so I decided to make a trip up the road. Nothing! It never made a noise during the entire trip. So, today I went out to install my new LED interior bulbs. I cranked it while out there & still nothing. My wife decided she wanted pizza for dinner, so I figured I'd take the Tahoe to pick it up. The whole way it was quiet as a mouse!
Needless to say, I'm still not sure what the issue is. Before we left for our Christmas break, it had been routinely chirping for about a month & a half. This occurred at both warm & cooler temps, as well as during wet or dry conditions. I'm just waiting for it to make noise again before I investigate further. I thought for sure it would chirp either yesterday or today.