Engine makes loud clicking noise at idle. on 2001 Volkswagen Passat

occurs when engine has been warmed up

3 answers 1 comment
Timing chain hydraulic tensioner do this very often. The hydraulic cylinder separates inside the housing. DO NOT drive the car like this, it could cause a serious damage. Beside this, the 1,8T engine is notorious about building up sludge, causing all type of internal engine problems, so I wouldn't be surprised if there are additional problems existing.
Find a good VW specialty shop in your area and let them diagnose it.

A 2001 Passat does not have a timing chain. So that is undoubtedly not the issue...
I can say, almost without a doubt that this is indeed the Hydraulic Cam Chain Tensioner.
It's hard to guess at the source of the noise without being able to hear it first hand and see if it is at engine speed or half engine speed, or if it internal to the engine or external to the engine. Check the engine oil level first. Definitely get it looked at even if it's just to see if it's safe to drive, if it internal to the engine (something starving for oil) it will get worse and more expensive to repair if left neglected. That engine it is really important to change the engine oil and filter frequently and use synthetic oil. I have seen these engines fail prematurely due to infrequent oil changes.