Last week I used my favorite sander, the RTS 400 for a little more than an hour and felt a numb, tingling sensation in my hand. I've never had that happen before with this sander. I did use my ETS 150/3 for four hours the prior day with no issue. Possibly, it's more an issue of user fatigue than sander, but I was wondering what other people's experiences are. Do Festool sanders tend to lose some of their vibration dampening over time? Thanks.