Subject: How do hover flies hover noiselessly ?

I would like it if you would tell me how Hover Flies a.k.a Flower Flies a.k.a.
Syrphid Flies,(Diptera,Syrphidae)fly noiselessly, when other insects don't. I
thought up some hypotheses. They are: 1. The halteres they use to balance their
wings enable noiseless flight. 2. They are preyed on by spiders like Goldenrod
Spiders. In order to avoid these spiders they must be very balanced,fast and
maneuverable. They move their wings very fast and the pitch of the buzzing sound
goes up so it it not heard. 3. Their wing are made so their movement causes no
turbulence. I doubt hypothesis answer one, since all flies have halteres and all
flies I seen so far buzz.I don't think halteres would work for that sort of
thing,and since flies don't have ears they would not try for their hearing's
sake. Number two,that they would fly fast to avoid predation, seems likely.The
fastest insect recorded is a fly.I do not know about the flower flies raising
the pitch of their buzz. I don't number three is the answer because their wing
veination pattern looks mostly the same as every fly (which buzz)and the
veination causes turbulence. Please tell me how hover flies hover noiselessly.
Thank you.    

Re: How do hover flies hover noiselessly ?