very loud clunking noise

Hey guys,
 
So I've noticed that when under load or when i rev my pinto a little higher than usual this small "ticking" or "clinking" was apparent from the engine, i mean when i'm heading up a hill and nearly flat footing it, or when i've got a lot of **** in the back (its a pano).
 
Anyways, so I'm taking off at a stop sign at a usual kind of pace and all of a sudden this bloody ticking noise just suddenly occurs and its really bloody loud! 
 
On the way home I noticed that the noise (apart from being very loud and worrying) only starts to happen when higher revs occur (not sure what revs, no tacho) but i'm not talking over 4 grand... also, there was no noise when engine braking...
 
A month or so ago I adjusted my tappets and checked everything twice or three times... made sure everything was tightened up, I don't know what the hell i missed... I'm very confused... Am I looking at some valve and piston interference here because it sounds like it to me!
 
Thanks in advance for any answers or wisdom.
 
Cheers

Hmm i thought about predetonation but would it have such a sudden onset as this? 

Cam timing jumped a tooth, check top dead on crank and if the cam wheel is not pointing direct south where the 'dot' is on the head, see manual, that'll be your problem. When a cam jumps a tooth it's kind of instant and rough idle if any idle follows

If it gets louder the more you put your foot down (especially at lower revs) and sounds like a very loud ticking sound (depending upon the size of the crack/break), then it does sound like it could be a cracked header or exhaust leak very close to the head (very common on a pinto).... Get a piece of vacum hose and put one end to your ear and run the other end round the extractors when the car is idling - to find where it is broken.  You will hear it with the hose, even if you cannot normally when it is idling) 
 
If it is worse at low revs but goes away at higher revs, could be a (slightly) bent valve.... 
 
It is remains throughout the rev range but just transitions from a ticking to a whiring gear type noise (not a good simalie!) then it may be a rocker has come loose or has bad adjustment (worse with bigger cams normally, but not too much that can be done in some situations).... 
 
If the noise suddenly stop and it feels like you are running on 3, then a rocker may have been being beaten to death and either broken in half or fallen off it posts (in pain)....
 
Unfortunately I have had all other than the last happen to me (I do actually adjust my tappets before the rocker gets beaten to death - but a mate who has no mechanical sympathy did it - and he was a mechanical engineer.  He only pulled the rocker cover off to see why it was no longer making a noise!!!)

Tim check that the spark plugs are tight.
PJ

Thanks pj and phoenix. Yep i took the plugs out and replaced and retightened when doing the tappets. Definately sounds like a top end prob.... my next port of call will be pulling the extractors off i reckon... i'll give it a run and see how i go then. 
 
Thanks guys

A cracked extractor (near the head) will sound like a ticking sound, and be much louder and audible to the naked ear easily when you give it more throttle under load.  The hose merely is like a stethoscope and allows you to hear it idling with no load/throttle... You need to move the hose around and under the extractors and all round the pipes to check everywhere...  A loose or cracked plug can also sound similar too, though should be a rare event...
 
The cam has not knocked a lobe off has it...???  You would have noticed a worn lobe hopefully when you had your rocker cover off if it had...

Hey guys so i did another test today, i took the extractors off and then whilst revving the engine, tightened the bolts until they were flush on the block... it seems that the noise comes on when the extractors are tightened up fully... I took a video so let me know what you think
 
http://www.youtube.com/watch?v=I8_XpP92fmg