Other: Which headsets to use in high EMI/ RFI enviroments

I have a customer who has an issue with the current headsetstheir spot operators are using where they pick up EM hum from the spot ballastwhen they are using them. I was wondering if you could tell me if any of the Clear-Comheadsets have any type of shielding of the mic element or use a humbucking coildesign? I've had a look at the spec sheet and on the solutions centre, but Ican't find any details other than the element is dynamic.
Currently our headsets do not have shielding for the actual mic capsule.Generally for high EMI areas we normally recommend using electret mic headsets.