That sounds like an issue I had with mine, was the tensioner making the noise, but there wasn't anything wrong with it, the belt was the wrong one, and it had stretched a little. The tensioner was reaching the end of its travel causing the noise.
A forum member stopped by the shop a few weeks ago. One complaint was belt squeal. A few shops had looked at it, had replaced the belt and tensioner, no change. Somehow these shops hadn't noticed that the idler pulley had vanished. It had been like that for a while.
That fix was pretty straightforward, lol.
Hino, not CAT C7.
For the running Freightliner M2 in my yard with 485k on its CAT C7, time is running short. It smokes some, sometimes pretty bad. I know it has at least one tragically bad injector. It may have low compression on one cylinder. The non-running M2 that's been chilling here for over a year may have an injector or two donated to the cause.
The owner of the non-running truck has been consistently screwing over the owner of the running truck AND me, so something something karma, something redneck justice. Or something. Maybe. We'll see.