Are you ready to let the first shop off the hook or is your intention to put this intermittent noise on them? If it was my car and I was doing the work I would first duplicate the concern but it sounds like this concern is already duplicated in your mind so I say the job should be re-done to the level of removing the new pads an cleaning them up or in the extreme a pad with a different composition. The cost of this activity should be on you but don’t let me discourage you from presenting the “pull the pads and clean them up” idea or the “change pad type” to the first shop.