Vibrate rocker/switch acting very strange

My iPhone 3GS vibrate/silence rocker is malfunctioning since I upgraded to the latest OS.

It may be a coincidence (the phone is now 3 years old and has taken a few drops in its time).

When I turn the phone into silent mode, the change doesn't seem to take effect (nothing happens) and then the phone starts randomly vibrating (going into/out of silent mode). And the silent mode never sticks.

I have two questions:

1) Has anyone else experienced this problem?

2) Any ideas what I can/should do?

Thanks, guys!