The T420 has a solid reputation and legacy, but it looks like I got a Lemon. I have had this unit repaired by EasyServe, but key issues, such as Keyboard flexing, plastics fit and finish, and general workmanship still are far below standard. Hopefully your System isn't as poorly put together as mine.
Update - Machine Was Replaced with a New Unit by Lenovo recently.
Recorded (rather hastily) on a HTC ADR6350.