I have 6 bay self serve about 40 yrs old with Ginsan equipment and Cat 530 pumps. Fairly well maintained. I can fix most any problem. I have 3 bays that run normal on rinse, but if you switch to high pressure soap or wax, the pressure falls drastically and booms go to shaking and noise in equipment room. The wax and soap comes out, but at a very reduced pressure. when you pull trigger, it shakes even more, also with loss of pressure. The rinse water comes directly off city water. When soap or wax is selected, that water comes from a float tank which has the wax and soap tanks on each side with hydrominders. Common sense tells me the pumps are fine since everything is good on rinse. Good pressure with no vibration on rinse. Check valves are fine where soap/wax goes into pump . This has been going on for a couple months. I need to fix it. I am at my wits end.