My FC just started making an odd buzzing/grinding sound that is coming from the speedo/tach area whenever I rev past 4000 RPMs. If I had to guess, I'm pretty sure the sound is coming from the speedo, as it stays quiet if I simply rev the engine at idle in the driveway - so the car and speedo needle needs to be moving for it to make the noise. Also, it seems to be independent of actual road speed but it resonates right around 4K RPMs, so if I mat the throttle at whatever gear I'm in, as RPMs start approaching 4K, the sound appears, peaks in volume at about 4K and fades off as I rev past 4K.

Anyone else have similar problems with their speedo or know of a solution to this?

 

Probably, your speedometer cable is lacking lubricate causing to bind. Try disconnecting your speedometer cable and see if the noise goes away.