That'* tough. I was certain that it was a rotating mass making the noise, but when I had an assistant recreate with me observing, I couldn't see anything rubbing or rattling. This drove me nuts! I was convinced the balancer was failing, but upon replacement there was no change. I planned on replacing the cat. But I had a credit at napa worth an engine mount, so I changed it snice it looked a little rough.
Anyway, to answer the question- I don't really have a solid answer! Only other thought is maybe the exhaust was rubbing. But it sure seemed to originate from the front of the engine.
Thanks again for the input everyone!