I guess it depends on how well he contains his energy. The latent buzz of electronics generally comes from charging devices that're full charge (side note, thanks for reminding me to unplug my phone). This draws current and attempts to send the same amount back, and when the electrical system can't do that (either due to the device not supporting it or having bad wiring at the port) the energy has to go somewhere. This is how light bulbs work, they turn that excess electrical energy into light and some sound (since energy cannot be created or destroyed, only transformed). In something without a filament to produce light, the conduits will begin to vibrate to remove that energy, creating sound waves.
How does this relate to xerath? Well, it comes down to a question of if he's constantly generating energy or simply drawing it from elsewhere, and if he has a reasonably met max capacity. If he's constantly generating his own magical energy and has a cap of how much can be stored, it stands to reason that if the cap is met then energy must be released. This could be done in lasers, but that's probably pretty inconvenient if he's in the middle of dinner or whatever ascended beings do in their spare time. More likely it would be released as light or as physical vibrations in his armor, making sound.
Meanwhile if he has no cap, or simply draws the magic from elsewhere, he'd have no reason to vent energy, and I doubt there'd be sound beyond air vaporizing due to touching his energy.