2004 Cadillac Escalade Serpentine oe AC belt

My Escalade has begin making a bird chirp type of noise and I was wondering if it was the fan belt or serpentine belt, when i got my oil changed i was told that i may have to replace a belt but i forgot which one, so i was wondering which belt it may be? the bird chirp sound will start in the garage since it has been cold then stop then start back up- also is this a very expensive fix?please help.


thank you so much for your time..
Navy lady 1972