Hello: A tool we use is a “recording pressure gauge”. It sounds like it would be the right thing for pinpointing your trouble. It records pressure on a circular, 24 hour graph. If there are regular pressure fluctuations, you’ll spot them this way. Short of finding one of these tools, get a normal 0-160 or 0-200 psi gauge and see if you can catch that pressure surge. I’ve used our gauge to spot malfunctions at the local pumping station, the utility didn’t know about.
I’d also call Rheem technical support and see if this is a problem they have experience with.