5870 Rattling Noise

I recently built a new computer, and noticed the case (Antec 300 illusion) came with a high def audio port built into the front. After plugging it in and trying it out, I noticed a weird rattling noise coming through the headphones. I tested the headphone jack built into the motherboard, and there isn't any rattle issue with it. I searched around a bit and found people having this problem with their graphics card, so I put my ear up to the case and, sure enough, I heard the rattling.

The odd part is that even when the graphics-heavy program is closed and there isn't any noticeable rattling coming through the headphones, there still is a rattling in the case, leading me to believe that it's something else.

Noise from the 5870 causing it would make the most sense, because the HDA port is much closer to the card than the built-in motherboard jack is. I really don't know why the noise would persist in the case when the headphones are fine, though.

Some extra information, the noise occurs to a lesser extent while doing non-gpu intensive things. (Web browsing, listening to music.) though it's often quiet enough to not hear it. The noise didn't occur when I watched a 1080p video in fullscreen.

I would like to fix the noise, but if it requires much messing around (Trying other graphics card, etc) then I'd rather just leave it since it's fine for listening to music, and I can swap to the other jack when playing games. I'm mainly just wondering if anyone else had a similar issue and found an easy solution.

Thanks in advance.

I know this may sound stupid but try blowing into the ports, see if it does anything. I would suggest RMAing it just to be on the safe side... but its up to you really.