Strange noise @WOT
 

I've noticed on the few occasions that I got WOT for
more than a second or two, I get this strange hissing/whooshing
noise from the back. It's loud enough to make itself known
over the B&B exhaust!

Imagine a big american car with carbs running without an air cleaner; you know
that 'hiss' they make when they throttle up? Kinda like that, but louder.

I have a vaccum bottle set up to supply the secondary plenum (964 engine)
and I'm thinking maybe I'm exhausting that and causing a leak?
Either that, or when you get a huge amount of airflow, and a large K&N,
you can get a noise like this?

This only happens when I stand on it for a few seconds at a time.

If it's more of a "whooshing" sound, my money would be on the K&N. If you still have your stock airbox laying around, you might want to through it on and see if the noise goes away.

Aha! Noticed that you have a 3.6 in that thing. What you are hearing is the resonance valve (i think that's what it's called) opening up via vacuum at 6000 rpm.I

It's kind of the pre-cursor to varioram. My C2 does the same thing. I have a drilled airbox, so you can really hear it when you keep your foot in it. I just love it!