Octavia VRS CR170 rattle/rumble at 800-1100rpm

Video here

Hi everyone, my 2009 VRS CR manual is making a strange deep rumbly rattly noise when it’s under load between around 800-1100rpm. The car drives fine and behaves normally though. Also no error codes. 

Bit of background, it had a newish turbo (and full service) about 3 months ago and had a new upstream lambda sensor a couple of days back. It seemed to start making the noise at around the time I got a warning light for the O2 sensor, but obviously carried on after I swapped it and stopped getting error codes. I do most mechanical jobs myself. 

Oh it’s also not the intake cover in front of the grille. 

Any ideas??

Thanks!!