How about building a small vacuum regulator instead of trying to
calm down the vacuum cleaner?

Get two leaf springs, two large pieces of plywood (about the size
of an exhauster bellows), and glue them as you would a bellows.  Cut
holes for inlet and output tubing and a final hole towards the bottom
which has a flap that is pushed open by a screw when it closes to
a certain point.

If you use leaf springs that were designed for a player piano, the
pressure should be the same roughly as inside the player piano at
maximum pressure.  If you want the pressure to be higher, screw in
the screw.  Lower?  Screw it out.

Good luck,
Eli Shahar

P.S.: Which Greek island?