Freeway knock??

[GTABurnout]

Well I went on a cruise with some of my friends who drive BMW's yesterday and well to make a long story short they love to open their cars up for some high speed runs. And I was more then happy to show them what I got. Well on all of the runs I was getting knock at like 80 if I leaned on to it hard. It was fine untill about 5psi of boost then it would walk up the knock guage. Is this normal? It only happened when I was getting boost and I had some race gas and xylene in the tank so it should have been fine.
Just wondering what it could be Thanks.

 

[trading t/a]

Prolly false knock! Driveline shutter. If it only does it at 5 psi I'd be skeptical. Gotta look at the plugs............

Pete