I've noticed that a few times myself. Most noteably badly grounded proaudio gear made the mics feel "rough" when plugged in. Its a well known warning sign that

I've noticed that a few times myself. Most noteably badly grounded proaudio gear made the mics feel "rough" when plugged in. Its a well known warning sign that something's amiss and could become dangerous.(1) I went so far as to make a little medium voltage amplifier and hook it up to my signal generator so I could try various frequencies and powers. Lots of strange and wonderful textures emerged but it always felt a bit tingly, like I was getting a mild shock. Hopefully they've figured out how to keep this from happening while still keeping the good part. (1) Every once in a great while someone is hurt or killed touching a microphone connected to a malfunctioning mixer/amplifier.