its a issue with the n73 due to design of the back panel. The loose fit leaves a slight space towards the top of the phone just over the camera on my n73ME and theres pretty much nothing you can do about it.
Frankly the N73 was never rated highly for its fit and finish. The creaks and squeaks when you type or hold the phone firmly are just lame ruining what is otherwise a very capable phone. Another sore issue is the unergonomic keypad and spacing. typing messages is a pain... literally especially if you sms a lot.