You may need to do a Burn In on the phone.
If it's not on warranty, and you don't really want to pay metro to return it, and get another one, try doing this.
Open the phone up, strip down as many components as you can from it, and remove the heatsink that's on the processor, then run it for about 5 seconds without that shroud on it (you'll have to put it back together to DO that, so this will take some time I'm sure.)
This will essentially "burn in" the solder that may be coming loose, and potentially causing this issue. A lot of times it's an issue with the flux that's in media ribbons throughout the device, however, and it's for that purpose I say the best way you can do a burn in would be to take a blowdryer or heat gun to it CAREFULLY.
Just because these things can take extreme heat when not on (upwards of 210c ) does NOT mean that you should apply that much heat to them at a close distance.
If you're not the risking type, then take it back to metro, pay them the little "swapping fee" and get another one on the spot.