It’s time to put a meter on it. Put your meter on manual ranging, (60v range) so you can catch faster fluctuations. I’m not sure if you said how long they go off for, or if they’re simultaneous. If it’s really fast, you can set the meter to Min. If you haven’t used Min/Max before, it will display the lowest value it has read and will beep each time it hits a new low. Very handy, I’ve even used it when I was by myself and needed to see if a card reader was closing a contact in the machine room. Land one wire to 24vdc, clip the leads from ground to the other wire, reads 0v, set to Max, go swipe the card and come back to see if the meter has seen 24v.