I've had similar weird sound probs, but it was because my jack wasn't securely plugged in to the N800!

I have a cheap headset that is supposed to be a good sound isolator, and it works great for when I'm jogging and don't want to hear much traffic noise. It's a JVC HA-S350, which cost me about $40 at Fry's. I wouldn't mention it, but I was unhappy with the last few headphones I got, and this is a perfect combination of cheap and effective. It doesn't have batteries, so doesn't do the real sound isolation that more expensive units do. But it works for me.