That’s a common issue… either you can search the web and fix it yourself, or try this out… You can get a free replacement.
http://support.ea.com/cgi-bin/ea.cfg/php/enduser/rockband.php
My drum kit was messing up (if I drummed really fast, like a string of red notes, it would miss hit and not hit every note) so I did the warranty thing. They sent me a new kit, I sent mine back. All better 