I'm getting a somewhat random knocking noise coming from the head of my G0704.
I can hear it at the upper end of the low speed range, but it's most obvious when I shift into the higher speed range and run up to max. speed.

It sounds like maybe teeth not meshing properly, or maybe something loose on a shaft. Hard to tell. It's intermittent.
I can hear it above the background motor noise but I wouldn't say it's particularly loud. I am concerned that it could lead to bigger problems so I'd like to figure it out before I damage anything.

I've been using the mill and it seems to be performing well. I'm getting good finishes. There's no slop in the spindle so I'm guessing it's not a bearing noise.
I've studied the diagram in the manual but I think I'm going to need to pull the head apart to get to the bottom of it.

Anyone have any experience with this kind of noise on their machine?

Thanks for any help on this.

Alistair.