Sometimes sounds are hard to locate.
But it sounds (no pun intended) like your tech is on top of it. All motors can sometimes make strange sounds when their bearings start to go. I can remember a lady that swore she had a bird making a noise in her's. Let him change it out and see if that fixes it.
"You do not merely want to be considered just the best of the best. You want to be considered the only ones who do what you do.".... Jerry Garcia
"You just have to decide if you're a Tigger or an Eeyore,..I think you know where I stand on the great Tigger/Eeyore debate." Prof. Randy Pausch