When a computer makes a loud humming sound and vibrates many times it is the CDROM spinning because it’s reading a CD. If you have a CD in the drive you should take it out if you aren't using it because the computer will tend to read the CD in the drive for various reasons.
If that's not the case then you may have a fan that is getting noisy or about to go out. There are fans in the power supply, on the processor and usually mounted inside the case. It’s hard to say which one it is without being able to look inside. You may want to open the case and run the computer to see where the noise is coming from. Other than that there are no other moving parts inside the computer except for the hard drive platters which shouldn't be able to vibrate your case.