William Meyer was asking for some help in a Welte Licensee upright.
The groaning you hear in the governor is usually caused by leakage.
Since all Welte systems utilize bleed drains to atmosphere for
establishing their vacuum pressure, the bellows most be very airtight.
Leather is not.
If the rebuilder who did the work were to remember that Welte used
a good grade of rubber-coated cloth in their system, then it would be
first wisest to ask "why" before deciding to improve it, and he would
spend five times the money that motor cloth would have cost. This is
obviously an attempt at an "improvement" of the system.
Leather never establishes a "fixed" leak -- it varies, according to
the pressure on it, since at low intensities (low pressures) it will
actually have less leakage, percentage-wise, than at higher pressures,
when used for bellows coverings. This is because the vacuum stretches
the leather a bit and pulls apart the fibers more. That means, nothing
in your upright has ever played the way it should, and the bleeds are
not really governing anything.
Get rid of the pneumatic leather and your groaning will cease. And you
might mention it to your rebuilder as well, so he doesn't think it was
just a fluke and do it to somebody else's.