Today I checked out my friend's 2001 S4. He is planning to sell it so I went to check it out today. I owned a A4 myself but really impress with the S4. Anyway, I opened the hood and I heard there is a clicking sound underneath the coverplate where I circled in the picture. What kind of valve is that? Is it normal to have the clicking noise or it means something is wrong? Many thanks in advance for all your help!!!

 

Mate it could be anything, we need more info,[sm=feedback.gif] betta pic maybe?

FYI there is several valves under that engine cover i think?

 

The N75 Valve is under that cover, meaby that's it ???
get that cover off and if the noise come from a black/brown switch with
3 hoses connecting to it, that's N75 valve. I dont remember hearing it
clicking all the time though. I'll check with mine today if i hear it clicking noise.