Windscreen Wiper Moves On Ignition

[otronics]

Hi.

 

Just successfully replaced the wiper mechanism.

 

A slight issue - when I turn on the ignition or start the engine, the passenger wiper now moves down and then up slightly, as if it is being tested.

 

The drivers side does not move.

 

Not a big problem as they both work but it would be nice to stop this.

 

Any idea how to solve this and why it is happening?

 

Thanks.