personally i can go all day washing with the lance or FSC and get no vibration trouble at all , but i do get after about 5-6 hours use a sort of electric shock feeling in my left hand ( i'm right handed) where it feels like someone has give me a sharp prod in my left arm with a pointed finger.
if you or staff are using a fsc and they are feeling vibration then your fsc is faulty as of which the cleaning ability will be reduduced and noticed, but as for a lance then it must be you personally.