Originally Posted by wstar

I don't know if rasp is the right word for it (seems to have some fixed connotations to some people), but there's definitely a vibrational noise at certain RPMs. I hear it pretty distinctly inside the car when driving, but I couldn't hear it much at all from outside when I was videotaping the dyno run. I think from the outside the actual exhaust sound drowns it out.

Being the paranoid worrier that I can sometimes be, my main concern is it could be a small leak that only opens up under the pressure of a loaded run (never hear it revving the engine in neutral), but the rational part of my brain says I've rechecked those bolts plenty of times now, and there's no leak. Most likely it's something else vibrating: perhaps something in the lower engine bay is rattling against the piping near the headers/cats, or perhaps one of those flimsy, thin undercar heatshields is vibrating in response to the exhaust, or something of that nature.

Anyways, I just got two more dyno runs scheduled today, one at the Dyno Dynamics place (Engine Logics), and a second run at the same DynoJet I used at the start of this thread (but will do it in 5th gear), so hopefully this evening we'll get some clarity on the numbers.