Go to practice mode and find any song with a long intro that doesn't include drums. I choose "Won't Get Fooled Again" by The Who and set the speed to 50%. This allows me to free drum for a long period of time, and you can hear the drums as you hit them. This also allows you to guage exactly how delayed the sound really is, but that's for another topic.
Now try fast rolls on every drum pad. Many people will report at least one pad, usually the red one, being unresponsive to the fast drum rolls/hits. Mine was only picking up every 4-5th hit so any song I played with a fast roll (tons of songs on expert) was losing scores and note streaks.
Possible fix with a US penny:
Possible fix by taping to reduce rebound effects on the piezo sensors (expand the "about this video" section to find the quoted text). Watch video to see how tape works, basically you're just tightening up the gap between the drum head and the body of the drum.
The tape is on my drums because the drums were faulty out of the box; the tape holds the pad closer to the sensor inside of it, which allows for more sensitive hits for the time being, until I get it replaced.
If one of the drum heads stops working, some people have luck messing with the piezo sensors themselves, which may have faulty/loose wiring. But this isn't a red/green drum roll issue, it's a "my drums are frickin' broken" issue:
There was an outstanding thread on the Rock Band forums showing actual voltage graphs for the piezo sensors, and explaining how rebound might affect that, but I can't find it for the life of me.