Xbox 360 doubled in sound coming from fan or disc drive?

i sent my 360 in about a 2 months ago because of constant unreadable disc error messages and when i got it back 2 weeks ago it was STILL doing it but 1 week on it hasnt had any problems at all, except for the increase in noise, the day i got it back and turned it on it seemed like it was taking off, as if there was another fan in there or something, anyone know why its like that?