Vibrations from a computer, which has moving parts, is 100% normal. Now if the system makes noise or the vibration is a lot there could be issues. You might have a bad fan, IE broken blade, bad bearing or lint on it. You could have a HDD that is going out. You could have a cd/dvd that is out of balance if you were using that at the time when you touched the case. Basically anything that is moving could cause it. You need to stop each moving part to find out what is causing it.