Is it gone when the engine is hot? If it does it then I would suspect the air pump pulley brg. I would not worry too much about it if it is the air pump pulley. If it is there even after the engine is hot it is one of the other pulleys on the front of the engine. May even be the alternator. Pull the belt and use a stethescope to try and determine which one is making the noise. At around 100k miles it may be a good idea to replace the idler pulley and fan clutch pulley.