My FW is "tingly" if I use the original foot pedal and plug the plug in backwards. If I reverse the plug, the "tingly" goes away. There's no "wide" side so I have marked it now so I know which way is which.
Interestingly, I bought a new replacement pedal that DOES have the wide plug, thinking it'd be safer, and the machine is tingly with it plugged in. I can't reverse the cord on that one!
I have yet another older foot pedal that fits the FW from another machine, that's new enough to have the wider plug side, and THAT one is non-tingly when plugged in properly. So I think the new pedal I bought is bad.
So it could be a problem with your foot, or if you're using an older plug it might just be in backwards.