I have heard this called preignision or detenation not predetenation,its more commonly called pinging or pinking,
sounds like a can of marbles being shook.Can be caused by too
high compression for the fuel being used or carbon build up,high
compression in a well used motor or baddly considered engine mods eg changes to the combustion chamber,or the timing is out
or the jetting is too lean.First thing to do is to do a compression test,this will rule out too high a compression,at a guess it should be arround 150psi to maybe 180 or so.Have a look at the plug,does it look white or worst case are there deposits, spots of stuff,BITS OF MELTED PISTON,on it,