A couple of weeks ago, investigating horrendous brake squeal I noticed both sets of pads had worn now to the metal and had badly scoured the rotas. Popped new pads in and cleaned the rotas but they had reached the point of no return.

So, new rotas and another set of new pads. Initially quiet braking, but both brakes are squealing like crazy again.

Any ideas?

Lube! mucho KY jelly?

RotORs

Your new rotors will not have any friction material ground into them yet. They may suddenly quieten down after a little more use.