In my 2009 Honda Fit with a 5-speed manual transmission, the transmission has a growl that starts at about 30 MPH and increases in pitch with speed. I used a stethoscope to pinpoint the source of the growl and it is loudest at the transmission. All the wheel bearings are quiet. My mechanic changed the manual transmission fluid, but the growl still continued.

Two mechanics and myself are stumped as to the source of the noise within the transmission.

 

Dirt/grunge in the axle cv's will do that..