Problem:
Our house in the city shares a common wall with our neighbor. At the
back of the house, our dryer vent is positioned about 8 feet from this
common wall. Nothing is wrong with the dryer according to a repair-
person and anyone's casual observation. The vent pipe is not
obstructed at any point. The exhaust vent fan (or dryer blower?) does
make a typical "whirring" noise which escapes from the vent and
resonates in a way which disturbs the neighbor. As crazy as it seems,
I now believe it's a legitimate problem for them due to the
configuration of the buildings and back yard.

Considerations:
-- I could possibly re-route and add to length of vent (limited by
dryer spec, of course), but would prefer not to. Besides, I'm not
sure it would help much by itself.
-- This is actually a dispute between our tenant and our neighbor, so
I'd like to keep them both as happy as possible. It's also been a
long-term problem.

Proposal:
My idea is to build a "sound-absorbing" box (approx 2' x 2') which
simply attaches to the building, over the existing dryer vent. I
don't want to restrict air-flow in any way, so the box would have to
have to have an appropriate opening for the air to escape. I'm
envisioning a simple box [a] lined with some sort of thick, sound-
absorbing foam, [b] having a hinged door to allow any cleaning/lint
removal, and [c] having a sufficient design to allow for adequate air-
flow.

Questions:
1. I know acoustics is a complex area. However, could something like
this actually mitigate the "whirring" sound of a clothes dryer as it
exits at the vent?
2. I've researched acoustic foams on the web. Any thoughts on what
types might work best for this application?
3. Would the placement of the air-flow exit hole(s) within the box
impact the efficiency of any foam?
4. Any other design elements (or other suggestions) which I should
consider?

Thanks!!!