Unfortunately, a gas fitter is usually not equipped or experienced with electrical noise issues affecting audio gear. Really not an electrician's realm either.
Fan probably switched by something as simple as a thermostatic "snap disc", probably up top/front.
Looks like:
http://www.pexsupply.com/White-Rodgers-3F01-110-3-4-Snap-Disc-Fan-Control-Cut-In-110-Degrees-F-Cut-Out-90-Degrees-F-14691000-p
Underneath, the louvres should be hinged or removeable. Look for something like this as the most likely culprit:
(about the same size as a dimmer switch... nudge nudge wink wink)
http://www.amazon.com/Suncourt-VS100-Variable-Speed-Control/dp/B004JYM2ZY
Fan probably switched by something as simple as a thermostatic "snap disc", probably up top/front.
Looks like:
http://www.pexsupply.com/White-Rodgers-3F01-110-3-4-Snap-Disc-Fan-Control-Cut-In-110-Degrees-F-Cut-Out-90-Degrees-F-14691000-p
Underneath, the louvres should be hinged or removeable. Look for something like this as the most likely culprit:
(about the same size as a dimmer switch... nudge nudge wink wink)
http://www.amazon.com/Suncourt-VS100-Variable-Speed-Control/dp/B004JYM2ZY