Is there a click when you open and close a tap. If so you have a micro switch so no pressure switch. If no click, there has to be a way of switching the pump on and off. Most likely way is a pressure switch.
if you have the switch on each tap all it needs is for one to be permanently on... then other taps on or off and the pump will be running all the time..
so its ether a faulty tap micro switch (could be any of them not the one you are using) or a faulty main pressure switch.. one or the other depending which type you have..
Are you using a Whale system ??? or do your taps have built in micro switches.
You can get a noise from Whale system, when you shut off tap pump carries on running to pressurise system is controlled by valve fitted with adjustable micro switch, Either screw down knob on teepiece while running cold water out tap or slack off till noise stops
IF you get it quite on cold should be ok on hot. Taps with micro just shut off 12 volt supply to pump. trouble with Whale system is pump keeps running if run short of water when tap shut pump cant pressurise system to open micro switch to cut off supply
I've done a bit of reading online and think it could be a faulty relay - as I'm sure it's microswitches, but the pump runs on whichever taps are used - kitchen, bathroom or shower.