I don't know how significant it is (the difference is about 5 dB at an airspeed of 130 knots), but CH-47s are quieter when loaded up.
https://www.researchgate.net/publica...my_Helicopters
Except at the highest speeds, sound variation with speed is not a large factor. In terms of sound variation with load, the CH-47D actually made less sound during level flight at full load than it did lightly loaded, although the sound did increase with load during takeoff and landing. As with other aircraft, the CH-47D makes more sound during landing than it does during level flight or takeoff