Although not on an AMT, I do have some experience of an engine making horrible sounds in flight, being hard to rotate on the ground, and yet not making any such sounds when run afterwards...

On my oldest P120, during one flight the engine started making horrendous screeching noises ; I immediately landed & shut down, then checked by hand to see if the turbine would rotate freely ; although it would turn, it caught at a certain point on each rotatoin , and bound up at that point. John Redman turned up about half an hour later, so I took the engine over to him .. and was surprised when it turned over perfectly freely. Matt Carrol came over & asked me if I'd been doing my usual hard snap-rolls during htat flight, and I conformed that I had. Form ta twe pieced together what had happened - during the snaps, the whole rotating assembly had managed to move just enough for the turbine and / or compressor to rub slightly ; that friction caused an instant heat increase, wihch in turn caused expansion which caused more rubbing, etc untlil I shut down. On the ground, the engine was initially still warm enough for the components to rub when I checked it over, but by the time John arrived everything had cooled down back to its "normal" fit.

Now, I'm not suggesting that snaps had anything to do with Woj's scenario here - just pointing out that it is in fact perfectly feasible to have an engine screeching etc, and then to have that go away when tested later. In my case there was visible eveidence of what had happened though, and about $45 later John gave it a clean bill of health.

Later,
Gordon