Just got a refurbished e420 for my wife. I've noticed the extreme right keys (Backspace, \, Enter, Shift, PgDn, Right arrow) don't have the solid feel of the rest of the keys and make something of a clunking sound when pressed (although they all work correctly). There's also quite a bit of flex in plastic plate underneath the keys in this area compared to the rest of the keyboard. Is this a common issue with this model? I know there's hollow space in the DVD drive bay below this part of the keyboard, but haven't encountered this kind of thing in similar lower-end Dell and HP laptops. It does cheapen the otherwise decent build quality (the refurb appears brand new).

I have the same issue with the e420 that I got for my wife for Christmas. I did not notice the flex until I looked for it BUT I did immediately notice the clunking sound on those keys on the lower right side of the keyboard. The sound is anoying and sound very cheap.

A folded piece of paper under the keyboard fixes it.

How about a general size of the paper and how many folds/layers?

Big enough to cover the affected keys, enough layers that they stop feeling/sounding clunky. At least four IIRC, but I have an Edge 15 and the keyboard is very warped (I was surprised the keys on the left side didn't have the same problem).