Ticking noises like this are very often associated with a failing fan bearing. The fact that there's a change in the sound when you tilt the case, does point to a fan problem.
Are we talking about a desktop machine? if we are, remember that there is a fan inside the Power Supply unit, as well as one on the CPU and possibly another one on the graphics card. if you open the case and lay it on its side when the computer is running, you should be able to locate the source.