True, but I have serveral and it woule be strange if all were broken 
straight out of the box =) 

-----Ursprungligt meddelande-----
> tapped the cover lightly and the output jumps an impossible amount,
> corresponding to several mm which it clearly isnt moving

The other possibility is that one of the other terminals is damaged where
it connects to the track. Any vibration would cause electrical noise, just
like a dry joint does

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