Loud rattle, possible exhaust leak?

I've had a noise I noticed since I've had the truck. When accelerating, I hear two separate and very distinct sounds. The normal revving of the engine, and what I would call a loud, regular rattle. By regular I mean it always sounds the same, and has a specific speed and rhythm. The noise gets noticeably worse the harder the engine is working. It sounds to me like an exhaust leak, but my mechanic skills end at changing breaks, so I'm not really qualified to diagnose the problem. My two friends who own Tacomas, both DCs, one an '06 Sport, one an '08 OR, do not have this sound.

I tried recording it for y'all, but my digital camera video mode doesn't do all that well picking up sound.

I took it to my Toyota dealership, and they agreed they heard the noise, but didn't know what it was. In order for the them to look into it further, I have to schedule an appointment with a district representative or something.

Out of curiosity, is Toyota obligated to spend the time finding out what this sound is, or since it isn't directly affecting the performance and function of the truck, can they just blow me off?

I'm embarrassed to drive other people w/out the radio on fairly loud because it sounds like a go-cart, not a bad ass truck...