X5 engine noise. - help!

[X5-mark]

Hi
I have a 2002 x5 3.0 petrol (with LPG also), recently it's developed a strange noise. It started as a metallic type chattering a few weeks ago but we picked it up from the airport after 10 days away and it seemed a bit worse, this morning it progressed to a knock? type noise, it was bad so i took a video and left the car on the drive!

Not sure if its possible a failed pulley could make this noise? The alternator was replaced a couple of months ago.

BMW x5 3.0 petrol knocking - YouTube

If anyone has any ideas please let me know.
Thanks

[740ilDuke]

Definitely not the engine. Sounds like a belt, or a tensioner pulley about to fail. When you revved the engine the sound sped up slowly. Inspect from the bottom up and really stare at each moving part.

[X5-mark]

Hi, thanks for the advice and taking the time to reply. I've not started the car since but I'll take the belt off at the weekend and see if anything is obvious.