As crazy as this may sound, but it has resolved itself.

I feel like - I think it triggered right after I decided to top the ~wax~ and did wax-as you rinse application. I even went ahead and did mineral spirits wipes, etc on each sensor, etc , thinking I had caused it .

It's been about 2-3 weeks since then and plenty HOT. Anyhow, it's raining cats and dogs today, and the looooong beep has disappeared. Eh, we'll see if I jinx it and if it's there tomorrow.