Took the car out yesterday to try and better pinpoint where the rattle was coming from. First, I discovered that the problem wasn't just on cornering, but even when going straight at a certain, very narrow RPM range. I could make it happen going straight and holding accelerator at about 1000 rpm in second gear. Under normal driving conditions I am just accelerating through this range and the noise wasn't noticeable. The noise was only in a range of about 100-150 RPM and really seemed like the whole exhaust system vibrating but more on the passenger side.
Back in the garage I crawled under there and started tapping around with a rubber hammer - checked all the clamp bolts. etc - nothing seemed amiss. the only thing I found was that the rearmost rubber insulator on passenger side felt somewhat looser than the driver side. After pulling it off I could see that the slot in the rubber where hanger passes through was a little wallered out and the hanger could move a little. I stuffed a small piece of weatherstrip in the gap and reinstalled the hanger.
Boom! no more rattle. Would have never thought that little looseness way in the back could create the sound I was hearing, but then again it makes sense - the rubber isolators dampen harmonic vibration in the system.
Really am pleased to have fixed this annoying problem - thanks to all for your ideas.
Kurt.