Karyn
It's either the highly carbonised rubber shock mount that has a strong piezo-electric effect...
or the idiot light..
I'm guessing it's the idiot light, every mic should have an idiot light 
people still don't use them...just last night we had rehearsal for upcoming Christmas Advent service and we have new people on the mics which aren't normally on the mics. you push the button and it turns green when it's on. if you push it again it turns amber for mute. if you push it again it turns off.
none of the new folks could just keep it on without further instructions. just keep it on, hand it to the next person. they would inevitably turn it off or mute before handing it to the next person...
