iPhone 3GS silent switch is not working properly

For some reason my silent switch is not working properly. It works fine when it is switched off (sound on) but does not always work when I flip it to silent mode. It seems like the switch is not moving far enough to trigger the "silent mode" even though the switch is totally flipped. And depending upon the orientation of my iphone (upright, on a side, upside down, etc) the phone will toggle between sound and silent mode. I have cleaned the area and still have this problem. Is this a issue that can be fixed or is it under a warranty. I have not damaged or dropped this phone in any way and have had it for a little less than eight months. Thanks in advance.