iPhone 3GS makes fast clicking sound during calls

For some unknown reason my iPhone 3GS has started making a fast clicking noise during phone calls. I only hear w my ear against the phone and not while using a Bluetooth device. Have also noticed that the power button at the top has become selective as to when it wants to work when I press it. Sometimes it powers off immediately sometimes it takes 3-4 attempts. Otherwise it is fine working order and have had zero problems previously. Is it possible the power button is going bad and has some relation to the clicking sound when my ear is against the phone? - Thanks