I seen this in a CR-V Forum concerning the above subject.

Noisy buzzing sound from under car
The tinny buzzing noise I was hearing at 2200 to 2500 rpm is fixed. Believe
it or not, the problem wasn't a loose heat shield, or a vibrating loose bit
of metal on the muffler, but the timing belt! It turns out, the timing belt
was set too tight at the factory. The service department simply set the
timing belt to factory specs and the noise went away. I must commend the
mechanic that tracked this down, because it really did sound like a loose
piece of metal.

Seems to me that if this were the problem I am experiencing it would of
shown up from the git go when the car was new!

Tom