Hi nixxy1983
It might not necessarily be dust, if it is under a year old, unless your home is incredibly dirty

Seriously, it could be a faulty fan or worse (if the sound is being generated by the hdd).
Speak to Acer support in your region, they should be able to advise you on the length of time for it to be in for repair.
A clean up of a PC, shouldn't take more than a few hours....