When you get a slight vibration or pulsation you want to remove the head and do an O & I (open and inspect) on the head. It’s easier to loosen the valves caps when the pump head is still on the pump. Once you get the head off the pump remove the valves, note the hole that each of the valves come out of. Inspect each valve for debris under the seat, valve springs for damage, “O” ring is not damaged or broken, valves last for many years, I can't remember when I last replaced any valves on our pumps. If the “O” ring is broken there’s a good chance the head is washed out on the valve side of the pump. Inspect the valve bore for any signs of damage, if the head is washed out there’ll be cut marks or grooves in the seating surface of both the valves and the seals. Once you have completed the inspection of the valves, remove the seals from the pump head. Again you’re looking for cut marks or grooves that have been cut into the seating surface of the seal. If your head is washed DO NOT attempt to put in new seals in a washed out head, you’re wasting your money as the new seals will be ruined in short order. The 5CP pump has a one time warranty replacement, if the head is washed out strip it bare and contact Cat pump.