Tools often have a safety pin on one motor brush , Makita grinder I recently changed brushes on had a tiny spring loaded pin ( none conductive ) this pops out when the brush wears down to a set limit and stops the grinder working before any damage can occur.
Motor may have been damaged , when you get metal to metal or slight gap it can create a weld spot on motor ruining it .Buzzing may have been something shorting out .
Did you take a pic of old brushes?
Agree badly worn motor brushes will cause trip as you have metal on metal shorting out.
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What a troubled life you lead .
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Post is a bit garbled but looks like you have employed chancers rather than pavers , if the blocks go in at the height set in photo the rain run off will be into the house thru the air vent shown in the photo causing damp and possible flooding breaching any dpc.