Tuned mass dampers are designed so that if the system starts resonating at its natural frequency it can dump it's energy into the damper instead of not dissipating the energy and shaking itself to death--assuming you're at that frequency for awhile. An analogy would be when your tires start to vibrate because they're not balanced, they've hit their resonant frequency and are holding onto the energy instead of burning it off (which is why it only happens at a specific speed, slower or faster and the tire is happy since its not at that specific frequency). Most things I've read is people don't notice any difference, if your drivetrain doesn't hit that frequency ever (or just for a small burst) then the damper never actually does anything, it's just their so in the event the drivetrain is held at it's resonant frequency it won't sit there vibrating like crazy and potentially breaking stuff.
