Drive Belt Breakage Cause-could it be AC?

Hello Everyone,
I am afraid we may have treated a symptom and not a cause. Our drive belt on our 04 Sienna would squeal for a bit on start up when the AC was on, but the squeal would go away after 15-20 seconds, or when driven. I had had two places check the belt when I took the van in for other services, and both said the belt looked fine and was under proper tension. This weekend the belt snapped while my family and I were out of state. Luckily I was near a Pep Boys, and AAA towed me there, and they put a new belt on for me. It is now super quiet- except: when driving at highway speed, about every 90 seconds or two minutes, I'd hear just a single chirp, and could swear I could feel it too. I had the AC on. After about 10 minutes of listening to this, I turned the AC off, and there was no noise. I turned it back on, and sure enough, the chirp was back, about every 2 minutes. My fear, is this something with the AC compressor, putting more strain on the belt/system than it should? I don't notice it driving in city traffic, but did notice that the interval between the chirps got longer as the sun went down, and the AC didn't have to work as hard. Any thoughts would be appreciated. Thanks!