Our S70 just started rattling from the left front as well. Doesn't happen much but when it does, it sounds like a metal muffler cover of some sort. Ground clearance on the S70 doesn't help much when troubleshooting.

Pull on the left side of your dashboard. If it moves at all, the nuts holding it on are backing off and rattling. They are located under the black cowling between the dashboard and the engine hood. I had this same issue on my 1998 S70. It sounded as though it came from near the left dash speaker grill area.

Hmmm>>>I recently began experiencing a vibration just as you describe, though I wouldn't call the noise "loud" but it is annoying. So far, all I know is that any of the following temporarily ceases the vibration for several seconds:

1) turn the wheel slightly
2) let off and reapply the brakes

I can't figure out the cause either, but I'm working on it...As of now, I suspect a brake caliper/pad problem, sway bar bushing, power steering pump pulsing, tierod end problem, something loose in the dash.

Good luck! Post if you solve this one...

Hopefully as long as you've alerted them to the problem, and they have documented that you had reported it prior to the warrenty running out, they should fix it as if under warranty if it reappears later on.

I had a similar problem with one of my vehicles. I noticed a intermitted problem when it had about 15K on it. The dealer was never able to recreate it. It kept popping up, but again the dealer never felt it. Finally, at around 60K, well out of warranty, the dealer felt it, and fixed it for free.