I saw the note when I arrived but noted that the lens holder was extended a bit too far and remembered the loud whistling noise it has been making not only when the laser is firing but continues for a few more seconds as if caused by the air assist. Sure enough, the air assist tube had previously been mended where the clear tube joins the smaller green(?) tube with masking tape. The masking tape had been pinched and had a hole torn in it, creating an unpleasant whistle.
Because it was only tape, I replaced the tape as I don’t think I’m allowed to do anything more significant. After the replacement, the laser (and of course blower) is as close to whisper-quiet as I have ever heard it and it is cutting through the stock I am using without any problems at my usual settings.
I suspect the issues you were having were caused by improper lens alignment and the lack of air-assist.