Everytime I bring to the dealer, I mention this, and they say it's normal after the engine heats up. They replaced the purge value I think it's called a whi le back, and you can still here this tapping/clicking at idle. I'm assuming this is normal?

 

Have you yourself, not your girlfriend, lift the hood and tried to locate the source of the noise-----what's the source???

 

Done this a dozen times and can't tell. 2 dealers day normal.

 

If it is serious it will get louder and easier to pinpoint. Until then I wouldn't bother.

 

Is the sound audible in the drivers seat? as if its behind the dash?

Or do you hear it outside under the hood around the drivers side of the bay?

 

Any chance can you film it ? At least some experts could give you a shot

 

I tried before but the mic can't really pick it up. Does anyone else notice this>?

 

Yes I do,its been there since I own car.
Apparently(according to the experts I have consulted) nothing to worry about.
There is a fix however:

https://mbworld.org/forums/s-class-w221/424944-s550-4matic-engine-knocking-tapping-noise-solve-mystery.html

 

Thanks, yea, I had a new purge value put on by the dealer, and ticking is still there.

 

Jason its time to trade that pos in bro!! LOL how u been?