300ZX Loud knocking noise after 2500-3000 RPMs.

[roshenu]

Hey guys
I'm new here but have been referring to this forum to have many of my questions answered. And today I have my own scary & frustrating question!
My 90' 300ZX with 123k miles starting making loud knocking noises after a kinda vigorous highway run.
It idles fine and no loss of power was noticed. But when you rev it close to 2500RPM a loud knocking sound occurs. Sounds like it was coming from the passenger side towards the front of the engine.

I ordered the 120K timing belt kit a week ago and the parts just arrived today. :@ I was hoping it would be the tensioner or idler pulleys making the noise, but many say they would only make ticking noises. Not metal knocking noises...
What other reasons could be the cause of this knocking? Is my engine toast? :'(

I found a few videos that might help explain my problem.
This is the behavior - http://www.youtube.com/watch?v=x89so4kLNUw
And this is the exact sound - http://www.youtube.com/watch?v=S1k7ZKzXbqM

Thanks. Any help is appreciated!

[itsa300zx]

May also be VTC springs in the intake cam gears, they should be part of the 120K kits.

[roshenu]

Would disconnecting the VTC solenoid be a quick diagnostic?