Help I can't sleep!

We just had an attic forced air gas heating system installed as part of
an addition. The heat system is FAR from quiet. The heating
contractor has already been back once and says he doesn't think he can
make it much quieter.

I have found by removing a vent cover that the problem is almost 100%
due to the air noise created as the air flows through the supply and
return vent covers. No covers, no noise, period. Right now he has the
supply covers as concentric square louvered vents, with a damper behind
the concentric squares. The damper is fully open. For the returns, he
has grills with 1/4" slant fins. These whistle like crazy and HAVE TO
GO.

I've asked him to slow down the heating fan (it has 4 speeds), but I
don't know which speed he has it on now. Obviously too low, and we'll
lose efficiency.

We're only heating one master bedroom (plus bathroom and walk in
closet) with this system, so I'm considering removing the damper
portion of the vents, as I don't think I need it.

Does anybody have a product recommendation for a quiet vent. The vents
are on 10" mount boxes fed by 8" flexi tube (I think).

Thanks,

-Jim Heck