I really can't see a brand new Pulley failing after a hour or two even if it is a old style one with the known failures. The odds are very very rare even the crappy ones last quite a few months before making the noise again.
Maybe get a spanner on the auto tensioner and put a bit of pressure on it (lightly pull towards yourself) and get someone to rev the car see if the noise disappears? With you on the spanner it will stop the tensioner from moving and making noise if that's the part that's failing.
Maybe get a spanner on the auto tensioner and put a bit of pressure on it (lightly pull towards yourself) and get someone to rev the car see if the noise disappears? With you on the spanner it will stop the tensioner from moving and making noise if that's the part that's failing.