Spindle seems to slow down near start of job

Hi - I’ve noticed on all my jobs recently that the spindle on my Nomad audibly slows down near the start of my job.

I did a test cut on wax - it’s really obvious from the video - not sure if these links to the specified times work with this forum’s embedding thing, but here, if you start watching at 0:30, from about 0:34 to 0:37 the spindle speed and audible pitch drops quite noticeably:

Here’s a link to 0:06 seconds where it’s free spinning (not cutting yet), with a significantly higher pitch than

this link to 1:17, where it’s also free spinning (not cutting, after doing a bunch of other cuts), with a significantly lower pitch:

I just did a few air-cut tests (no stock) and I didn’t hear it slow down - not 100% sure that’s repeatable, but on my last ~10 real cuts it seems to slow down. Interestingly, it seems to only slow down once - it’s not like contact with the stock slows it down more and more and more over time - just once to a lower pitch and then it stays there.

Any ideas? Could there be a loose wire or something in there?

BTW, gcode is here.