Pressure switch slowly falls below cutoff and remains at around 40psi

[homer12]

Hello forum,
I have a water filter downstream from the waterpump that feeds the house.
Recently after few months of operation I heard pressure noise coming out of the pump.
I tried to adjust the pressure switch and then the switch went firing repeatedly turning the pump on/off rapidly.
I did some googling and I took the filter out. Run the water out of lines and tank and pressurized it but not sure why the tank will not take more than 28-30 psi.
I started the pump again and I adjusted to 35-55.
The pump now builds up to 55psi but with time it drops to 38-40 and stays there.
Is there any common remedy/troubleshooting before calling a technician?
Cheers and thanks for your input.

 

[Valveman]

Both the rapid cycling and pressure dropping when no water is being used is most likely a check valve or foot valve problem.