2000 Grand Am SE V6, 189000 km- alternator dying?

I recently was told by my mechanic that the alternator was what was causing noise on start up of the car. He told me it was still safe to drive and not causing any further damage to the car at this time. Is it really safe? Will the alternator making noise necessarily mean the battery will be drained? The gas gauge and speedometer, and radio lights are dimming occassionally as well- I'm assuming this means the battery is starting to go however there seems to be no problem starting up the car (other than noise).