As the title says, there's like a rattling or a ticking sound that is periodical on idle only, but only at around 750 rpm, if I slightly push the fuel petal the sound won't come at all. 

It's a 2007 TDI 2.0 BKD engine

https://youtu.be/tuVRXUwD_uo

Forgot to mention that in the video it's near the end 

Anyone who has any idea what it could be? It is coming from the right side in the engine bay 

Even with headphones it was difficult to discern.

 

I suspect it's a heat shield around the exhaust system come loose due to corrosion.

18 hours ago, MicMac said:

Even with headphones it was difficult to discern.

 

I suspect it's a heat shield around the exhaust system come loose due to corrosion.

 

I had a deeper look with my brother listening for the noise, and it seems to be sync with the lights flickering/dimming very slightly, so I am guessing it could be the alternator pulley going bad. It does only happen when the car is in Park or Neutral

An auxiliary belt is cheap and relatively easy to change, this would be my first attempted fix.

 

Assuming it has never been done, and given your location, I'd say a 13 year old belt that is under load most of the year would be something to replace preventatively anyway.

Naturally the alternator output will vary slightly at idle rpm especially with a tired battery/electrical loads on so the lights/noise are related to engine speed.

 

I've often used a length of garden hose to pinpoint sounds, with one end to your ear just be careful where you poke the other end around a running engine.

Forgot to update, but if anyone is interested it was a DMF going bad. I had it replaced.