@Torgeir If I move the extruder manually, the sound is still there, but only during certain types of moves. For example, on the X axis, it will sound horrible going left to right, but right to left there is no sound, just that silent humm you mention. There is also no play on the extruder, however the sound seems to be coming 99% from either the small motors or the belts, specifically in the corner of the printer. There is no real sound coming directly from the extruder. They have been printing quite a lot. I can't say an exact number, but since Sept 2019 they have been printing about 30-40% of the time, so let's say about an average 8 hours per day - times about 5 months, you get the idea. However, that's the reason we went with the not quite cheap Ultimaker S5's, on the premise that they can and will work that much.
@NovaStarGX That sounds like a plausible scenario. Can you please explain a bit more how you fixed it? I can't seem to quite understand.
Thank you both for the answers.
I had a very similar issue when I received my S5 last week.
My problem was the X rail guide had a 9mm difference from either side of the machine, and so the head was not exactly centered on the shaft.
What I did was turn off the machine, bring the rail far forward as possible, then used the machine housing as a reference point and measured the distance from the guide rail to the edge of the machine.
I literally pushed the black belt holder on the X axis to where it was parallel to the other side. That centered the head and now no noise.
Mind you this is a $6k machine that you won't expect to have these problems. The dealer said it probably moved in shipping. NOT A CHANCE. the X axis was strapped in with a cable tie, and with all the foam packaging ....
Anyway, check to make sure both axis are parallel. I founf if you're slightly off parallel you get weird noises coming from the machine as the head moves around