Pump intermittently kicking on

[TCL]

Recently my freshwater pump has begun kicking on for about 2 seconds every 5 minutes or so. It did not used to do this.

My system is two tanks, PVC tubing to two individual Sch.40 PVC ball valves so I can select which tank is used at what time, PVC tubing to the pump, an accumulator tank, then downstream to fittings, etc. This pump cycling thing is happening regardless of which tank valve is open.

My question is whether I should start my search for the problem downstream or upstream from the pump. I spent a lot of time for the first few years dealing with air leaks in the system (generally upstream from the pump), but that has been (apparently) all fixed for quite a while now. I can't logically figure out whether the pump would be kicking on to compensate for a loss of pressure upstream (like air leaking in) or downstream (like a problem with the accumulator tank) from itself.

Thanks in advance.
TCL
S/V Tallawah, 1979 Morgan 461