humming and clicking car

[gshane]

My 2003 Mercedes C240. is having a humming noise that would stop in few minutes but when the car is in motion it starts clicking. what could it be

[faheem]

If no other problem other than these humming and clicking u hear on very quiet road. Forget it.

These modern cars loaded with sensors and relays that keep adjusting and clicking many things while driving. If not really LOUD and IRRITATING its not a fault, its the way car has been build. take it easy and enjoy your car.

[adnanJ]

This humming noise is secondary air injection pump. they become little or more noisey at starting time and after that its fine.

If it fails completely if will light up chk engine light too. Get it proper diagonstic.