Apple iPhone 3GS

Here lately, I've noticed my phone vibrating in my pocket. So, thinking I'm getting a text or call, I take it out of my pocket to check. No messages or calls. Then, I noticed that I can barely touch the vibrate button on the side and the vibration goes on and off repeatedly, even while it's still in the down position (turned off). Is the button damaged, or is there something else I can do to fix it?