I agree with Robbie Jacob that the problem is usually in the regulator
on top of the pump.  The key, as John Tuttle shows in his excellent
description on his web site, is that the sliding lever is used only to
adjust the soft play level.  If it doesn't play any louder when switched
to medium or loud, then you have trouble with the four external valves,
or the stack is getting leaky and the pump can't keep up.

Robbie's idea of adding a motor speed control makes sense as it gives
a full range of vacuum levels, instead of three.  The motor can then
run slower, keeping it cooler and quieter, and also extending its life.

If you need a new vacuum box that would allow for multiple inlets,
we offer a unique design that allows for this.  All of the vacuum boxes
offered today have the motor jammed all the way at the top of the box,
such that adding a fitting is impossible.  Our 'Bergytone' boxes are
designed such that there is a vacuum chamber between the motor and the
box lid which acoustically dampens the air noise.  Because of this
chamber space, additional holes can be drilled in the top or side of
the box to accommodate multiple inlets.

Keep us in mind if you are looking for replacement speed controllers or
custom suction boxes.

Respectfully submitted,
Eric Bergstrom - Bergytone Products
http://www.pianoproservice.com/