Was the noise evident at the luthier's workshop, and they couldn't resolve it there?
Or, we're they never able to reproduce the problem you were encountering, and unable to establish a cause - only for the problem to return at your home / studio?
Again, is this problem only exhibited at your home / studio, and not at the luthier's workshop?
There are any number of reasons why your building (lighting, wiring, etc) could be the cause, but furthermore, the devices you're connecting the instrument to could also be the cause (pedals, amp, recording device).
It's quite possible for an otherwise clean signal path, to have high frequency electrical noise introduced depending on how the audio interface is connected to the computer, and how the computer is earthed / grounded.