Bosch motor whirs briefly when changing gear

[Fitcaz]

Hi,
any advice on Bosch gen 2 active line recent problem. When I change down gear the motor whirs quickly for a second or so then resumes normal operation. This has just started happening and otherwise the bike is fine. Is it a failed sensor and is it easy fix?
thanks

 

[Fitcaz]

Bosch dealer says new motor. €500

 

[bobcat931]

Bummer. The Active Line on my Cannondale Neo began making crunching sounds. New motor required to the tune of $900+ including installation.