Weird keyboard issue
 

Hey, any of you tech savvies wanna take a crack at this mystery? One of the keys on my keyboard is acting up - if you press it pianissimo it sounds like you hit it with a sledgehammer, but if you hammer down on it it sounds like it should when you press it gently. It's a Yamaha PSR E403 if that's any help. So. Yea. Any input on this would be great!