Alert sounding randomly/inexplicably in PP

I've seen numerous posts on this issue on the PC, but I'm on a Mac running Sonoma 14.6.1 with PP 24.6.1. 

When I start up PP, I get an alert sound. I think it's one of the system alerts but it's not the one I have chosen as default.

It sounds almost every time I switch to PP. So, yes, it's driving me crazy. Is there any solution for this?