Well I went and started up the burb at the mechanics parking lot. He hasnt taken it in yet, so he just did a visual check. No squeal, knock, whatever. I swear, hand to god, it sounded like imminent failure last week when I started it up. I tried it with both the HVAC off, and on, and no change...just purring right along. So, hopefully it is a tensioner, or a compressor in a worse case scenario. I cant imagine that an awful engine that is teetering on failure would sound terrible one moment, and just fine the next....so fingers crossed it is indeed a simple fix. He also assured me that it would be pretty strange for the 6.0 to die at 144k.
I am also having him check a knock/clunk/noise from the back passenger side. Something to do with the leafs. I posted a question in suspension a while back and no one responded....likely due to it being a 2500. I rented a lift a few weeks ago and found nothing loose so I'm not sure what the problem could be....mechanic will look at that too. That said, I took it to carx, and another shop to have them look into that rear end noise...both said they found nothing wrong, but its there, and it sounds like a loose tin of some sort. I figured I bumped the exhaust head shield or something, but nope, its secure.