<warning>this post is influenced by my finding a website selling USB cables for up to several hundred dollars.... seriously, some copper wire and various dielectric materials... several hundred dollars. This isn't a laboratory grade multi-gigiahertz RF cable here. I am shocked that such a company is able to stay in business selling cables like this, i mean shocked that they have a customer base to support themselves.</warning>
You are absolutely correct about not hearing the digital cables. Any who claims to hear the difference between USB cables (which are compliant to the specification) just doesn't understand how these digital communication systems work. And before anyone says... oh but you can hear the jitter, guess what... the serial signal is buffered, converted to parallel, and clocked out with a different clock. So no you won't hear varying levels of spec compliant jitter on the serial signal. And you won't hear any noise on the digital signal (unless it causes bit errors, but that sort of noise isn't going to be the fault of a spec compliant cable). So as long as you purchase a cable which is verified to comply with the USB specification (and that cable is not defective), the received signal is not going to have any bit errors, and bit errors are the only thing you could possibly hear.
I would even say that you will not hear RF interference from either the cellular signal or the WiFi signal, or the bluetooth, or any other RF communication signal (think about those frequencies and the limits of human hearing... Sure there could be mixing and downconversion, but the devices processing the audio signal aren't going to be efficient enough at RF frequencies to yield audible signal levels form mixing). Now what you might hear is switching noise from the power consumption as those devices turn on and off attempting to save power (they would probably switch off at rates varying from uS to longer durations, and 20kHz is a 50uS period). So while it might help audio quality to put your device in airplane mode, it isn't because of RF interference. And if it were you would hear those effects all the time everywhere in the world (you would be surprised at the RF noise that laptop power supplies can emit, not to mention your microwave oven running at those same frequencies, and countless other ubiquitous sources).
Just my $0.02, but I do design analog and digital communications systems for a living