Noisy freedom 20 inverter ???

Have a noise coming from my inverter area when on shore power.
Sounds kinda like an air hammer going off for a short duration.

Started about a year ago. It randomly sounds off for less than a second and may do so anywhere from 10 minutes to over an hour apart.
Does it on both 30amp and 50amp service.

I haven't had any problems with the electrical so I'm wondering what this could be.

It is such a short duration and random noise, it is very hard to figure out what is going on.

1997 CC Allure….
Freedom 20 inverter

OK, what else could it be???

Any comments appreciated… :h

.