Mori Sl3h clunking during speed change when running G96

Does any one else experience a clunking, possibly transmission clunk when running g96? It happens when changing speeds after slowing down for a larger diameter and then spinning up again right before heading back into a smaller diameter. Occurs even with small moves in the x when changing rpm.
Another shop has sl3 lathes also and they make the same distinct noise. My shop is smaller and perhaps that is why it is more noticeable. I have pulled the transmission out and cannot find anything that stands out, loose keys etc. Is it simply the case of a older transmission?

Any thoughts on this would be great.


Mark

Keyway on one of the clutch packs probably.

My Sl-400 does the same thing. It is more noticeable when in manual mode. It is because the gearbox.