Water pump on fiver periodically pulses

My water pump, which seems to work great as far as pressure and volume, every few seconds, maybe every five or so, slightly pulses. You hear a slight thump and the lights flicker just a slight bit. I’ve definitely determined it’s the pump. Turn it off, and the thumping quits. It seems the pressure drops just a little, just enough to kick on the pump which immediately applies enough pressure to shut it off again. I am virtually positive I have no leaks, which would have explained the problem. There’s no sign of a leak anywhere. So I’m wondering (first, do any of my thoughts thus far seem right) is there possibly a check valve that would allow water to flow back into my freshwater tank, just a little, just enough to relieve a little pressure in the pipes and therefore momentarily turn on the pump. It only turns on for a fraction of a second. It really sounds just like a bump. If so, is the check valve in the pump. It’s one of those SHURflo Revolution pumps that I put in five or six years ago to replace the OEM 4004 pump. It’s just started this recently.