yesterday it would'nt rev - why? This happened after my wife ran out of gas .

it very well can be that depending on the severity of the ticking noise, if it sounds like its coming from the top of the engine, place your hand on it when you start it up and if you can feel it knocking slightly and if the noise dies away once warmed up i'd say its your lifter, if its a heavier knocking rather than a ticking and comes from below or bottom end of engine it may be big end bearing, not good. try putting some engine treatment through the engine oil and make sure you run it in as directions state then change the oil and filter and see if that helps
or
It could probably the power steering pump.

First, I take the belt off and run the engine (For just a second) to make sure the noise ain't the engine itself.
I changed the Power steering pump and the problem(noise) went right away. TAKE THE BELT OFF TO MAKE SURE IT IS A BELT DRIVEN PROBLEM!!

sometimes the engine supporting structures become weak with time and that could be a reason

but make sure you also seek help of a certified technician
hope this helps:)