Strange noise - 2006 Honda Civic

I have a manual transmission, and when the RPMs reach approximately 2.5k in any gear, I hear a very high pitched noise. It sounds electronic if that makes any sense…the best way I can describe it is that it sounds like the high-pitched noise you sometimes hear coming from a TV or computer monitor when turned on. It also reminds me a little of a noisy transformer you may hear when walking down the street. It’s not TOO loud, but it’s loud enough to annoy me to no end.



I’ve taken the car in to the shop once to have it diagnosed, but the noise doesn’t happen every time you drive the car, and they weren’t able to reproduce the problem.



One side note is that the RPM range this happens during seems to grow slightly larger in higher gears. In first gear you might just hear a tiny blip as the needle crosses the 2.5 mark. In 5th gear the noise will sometimes last all the way from 2.4k to 3.2k or so.



Also, the noise will start and stop when I lift my foot off of or put my foot back onto the gas pedal, but I just assumed that was due to the change in RPM.



The dealer I took my car to said they hadn’t heard of that problem before and hypothesized that maybe it was a couple of pipes rubbing together, but I have no clue if that’s even a legitimate guess.



Any thoughts?