A vacuum won't do a damn thing. You need to use high pressure compressed air either from a can or air compressor. If the fan is loud however, it's probably not going to do a lot of good to blow the dust out but it can't really hurt. Loud fans (If you're talking abnormal noise and not just running at max speed) are usually due to failed bearings in the fan. That would necessitate replacement of the fan. Have you monitored the temperatures to see if the unit is overheating and causing the fan to run full speed?
Try HWinfo or CoreTemp to check the temperatures. If it is overheating you probably want to get it apart to clean it out and repaste the CPU/Heatsink or take it to a shop so they can do it for you.