I’ve noticed a tone consisting of harmonics of the two 400Hz unlocked engine generators on the intercom and RT transmissions of the 737’s I now fly, which the Airbus did not have.
I should imagine that the more modern audio circuits on the Airbus have better design, filtering, de-coupling, earthing and much higher common mode rejection ratio than the aged Boeings. The latter is the ability of an audio amplifier to reject unwanted noise and interference on it’s input. De-coupling, filtering and better earthing reduce the effects of noise, interference and ripple present on the power supply lines to the amplifier.
Also, lots of the Airbus wiring loom is contained in screened cables which prevents interference between parts of the electrical system - I don’t know if Boeing’s wiring is.