Today a Lockheed C130 passed where I work at cruise altitude. On the ground, the engine noise was very loud comparing to passenger jets. Even the Transall seems to be more loud then other jets. It looks for me that turboprops in general seem to be much more louder on the ground when they pass by on cruise altitude.
Did you guys notice something like that as well?
Does it come from the propeller- tips, which reach supersonic speed?