Probably Emergency Lane Departure warnings. I've been getting some of these - loud boing and red warning on the screen. It seems the latest update made the system a little over enthusiastic. You can turn them off in the Autopilot settings as your in the States. In the UK we can only turn them off for the current driving session, then the bloody things turn back on.
Agree with cgiGuy on the speed warning. Next time you drive see if the sound coincides with the speed limit sign getting slightly bigger (not their best UI decision there). Mine was on after my HW3 upgrade. I turned it off so long ago I didn't even remember it was a thing. Took me a while to figure it out.
Thanks everyone for the replies. I noted that I had the Speed Assist Chime enabled (Ref Page 114 Owners Manual). I disabled this 'Feature'. I haven't driven the car yet, but hope this change solves the problem.