[s-cars] Bypass valve question

[Joel Rector]

I have had the Bosch Sport Valve 110 in my 93 URS4 with MTM +1 for about
2 months.  On downshifting/engine braking I am hearing a high pitched
whine for a couple of seconds and it sounds like it might be coming from
the bypass valve.  I'm not sure though, since it only does it while
driving.  Almost like the sound of the diaphragm vibrating/flapping very
very fast.  The same sound you get when you put a blade of grass between
your thumbs and blow to make noise.  Has anyone else experienced this
before with a bypass valve, or heard this type of noise at all incase it
isn't the vavle?

Thanks,

Joel Rector