Considering it is so new you could consider doing a reset as follows.
Try doing a hard reset by following the following steps
1: Back up important data such as contacts, messages etc
2: Turn off the phone
3: Hold down the star *, green phone and number (3) key
4: Turn the phone back on with these keys held in
5: Wait for the device to start up completely
Restore back-up and try phone again, if the problem is still noticeable take it to your nearest Nokia Repair Centre
Your phone should be under a 7 day exchange warranty of some sort so you could consider taking it back to the place you bought it and trying that.
iPhone 4S 16GB
MacBook Pro 17" Mac OS X Lion 10.7.3