Two things you can check:
The central ac unit may have a problem such as a faulty compressor (overheats?), pull-in contacts, loose wiring on the motor, loose wiring in the circuit (wire nuts, j-boxes, etc), loose fan belt on the blower, or a bad low-voltage transformer. I would bet on the contacts that pull in the blower line voltage.
The work done by the electrician. Each circuit have its own neutral home-run? Sometimes they'll cheat by grabbing the nearest white wire. Big no-no.
All motors cause transients and surges in your house power system. The above can make it worse, in terms of hearing the noise in your gear. If everything checks out ok (including your gear), then you may look into getting a whole-house surge suppressor (TVSS) installed in your main panel. I also agree it ain't a grounding issue and that dedicated circuits are not the cure-all for power problems.
The central ac unit may have a problem such as a faulty compressor (overheats?), pull-in contacts, loose wiring on the motor, loose wiring in the circuit (wire nuts, j-boxes, etc), loose fan belt on the blower, or a bad low-voltage transformer. I would bet on the contacts that pull in the blower line voltage.
The work done by the electrician. Each circuit have its own neutral home-run? Sometimes they'll cheat by grabbing the nearest white wire. Big no-no.
All motors cause transients and surges in your house power system. The above can make it worse, in terms of hearing the noise in your gear. If everything checks out ok (including your gear), then you may look into getting a whole-house surge suppressor (TVSS) installed in your main panel. I also agree it ain't a grounding issue and that dedicated circuits are not the cure-all for power problems.