My macbook pro is making crackling noises

Was using Sketch Book (drawing app) and noticed my laptop was making crackling noises? My laptop gets hot when I use the app, (some times it over heats) but I've never heard it make these crackling sound before? Sounds like it's coming from either the speakers or where it blows hot air to cool off. Does anyone know if the crackling is related to audio problems or over heating?