[V8] Broken Wheel Bolts

[Kneale Brownson]

Anybody faced this before:
http://www.pbase.com/kneale_brownson/image/39122017  Those holes you can't
see through have broken-off ends of wheel bolts in them.   The broken bolts
are at    http://www.pbase.com/kneale_brownson/image/39121870

I was wondering why I was hearing a strange noise.

The Bolts were tightened by hand and torqued with a torque wrench, a
process I've done many, many times.   I checked bolt tightness again after
about 100 miles of driving.   Nothing was loose.

Any guesses as to why the bolts broke?

Any suggestions for removing the broken off stuff?  Since taking the pix I
have bathed them in Kroil.  I have a set of those reverse drill bits with
extractors.  Do I need to be accurate in centering one of the bits?  The
exposed surfaces are uneven.  Should I use the largest size I have?