Try 1000, if that's still problematic try 2000, then 3000 and 4000.
Something else worth trying is running the PC from a separate socket as far from the machine as possible via an extension lead, don't ask why but this does work, I swapped the mains feed to the 1hp VFD on my little CNC mill to a socket 5m away and it eliminated the noise issues,
Regards,
Nick