I don't know what's available to you but if you can get some chassis dyno time that's a great place to run the car while you poke around to see where the noise is coming from. I've used something as crude as a broom handle to reach under and poke a heat shield to determine if that's the culprit. Running a car under load reveals a lot of stuff you just can't find any other way shy of running down the road next to the car (I'm not that fast!). Locally I can get a few minutes pretty cheaply - as little as $60/hr. and he will sell me a part of an hour. You can grab your peak wheel HP while you're at it.......

Dan