From shawk, Post 521: " Unusual acoustical standing waves in piping can restrict fuel flow"
Interesting thought: The 777 uses a 'new' acoustic based fuel volume measurement technique. Presumably a pure ultrasonic tone is far more likely to set up a standing wave than the white noise from a vibration source, unless of course the designers had already thought of the potential problem and use frequency agility based on prime numbers?
I guess such a standing wave would only occur at particular resonant path lengths dependent on air and/or fuel volume shapes. I'm not sure if short wavelength standing waves would restrict fuel flow, but they would cause cavitation, as happens in ultrasonic cleaning.