That squeak in your video is exactly the same sound my truck made when that bearing went out. I hate that sound now.

As for how a diesel should sound, the above video sounds better then your first video, but to me diesels all sound sort of like a cross between a jalopy and a regular engine with a knox problem. I'm sure you'll get it figured out and have it running perfect. The prior owner didn't give you any clues to the condition of the engine?

Sounds like is has a miss in a cylinder or a sticky valve.