[toufiqbarhamov]

Not impossible, just impractical unless silence is incredibly important. If you want a quiet helicopter then you do what you can to reduce the noise signiture, then you might consider destructive interference. You wouldn’t use speakers, but that’s not the only way to produce a noise. In fact a clever country might even figure out how to use an arrangement of blades and fans designed to produce noise in such a way that it tends to cancel out the loudest contributions to the signature.

Buuuut... that’s not really viable for anything civilian or even commercial.

[odorousrex]

Like the Stealth Black Hawk helicopters that were used in the Osama Bin Laden raid!

(There existence is still not officially acknowledged of course, but many pictures exist.)

I was very curious about the technology they used to reduce the noise, as black hawks are very loud.