I'm not an engineer but it sounds to me like your pump is noisy because
it's running no load. ie) You said it forms "an air lock".

If this if true then the motor will wind up to no-load speed, which
could be several times the working speed.

Make sure the pump always has water in it (its primed) by routing the
intake so when it shuts off the water left in the line will run to the
pump impeller housing instead of bleeding back to the intake.

If it now winds up until it starts to draw water up the line and then
slows down under load.......you have the above problem.

been there and fixed that one