bad noise when awaking from sleep

So the past 2 days when i open my macbook pro for the first time of the day it makes a bad noise. this noise is sounds like it could be fans. the noise is coming from infront of the f keys which i believe is where the fans are. it went on for a good 20 seconds yesterday then today i tapped in front of the f keys and it went away. has anyone else had a similar issue and if so is there any fix for it? would dust buildup on the fans cause them to be off balance and rub on something in there? even worse could this be my hd ready to go? im not really sure where inside the computer that is located. its a 15 inch core 2 mbp