I put this on a while ago but if you really want to know what can cause ticking in the top of your engine, here is what GMH has to say.
VALVE TRAIN
A light tapping at one half engine speed, or any varying frequency, can
indicate a valve train problem. These tapping noises increase with engine
speed.
Before attempting to judge valve train noises, thoroughly warm up engine.
By doing this you will bring all engine components to a normal state of
expansion. Also run the engine at various speeds and listen for engine
noise with the hood closed while sitting in the drivers seat.
If the valve mechanism is abnormally noisy, remove rocker arm covers and
use a stethoscope to determine which valves or valve train parts are
causing the noise.
Valve train noises may be caused by one or more of the following:
1. Broken or weak valve springs.
2. Sticking or warped valves.
3. Bent push rods.
4. Dirty, stuck or worn valve lifters.
5. Damaged or improperly machined camshaft lobes.
6. Insufficient or poor oil supply to valve train (low oil pressure).
7. Excessive valve stem to guide clearance.
8. Worn valve guides.
9. Worn push rods.
10. Worn rocker arms.
11. Broken rocker arm stud.
12. Loose or worn rocker arm attachments.
13. Missing or mis-positioned lifter guides.
Enjoy