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

Blown head gasket between two cylinders?

To check do a comp test and if so the two offending/ adjacent cylinders will be down on comp, usually but not always by same amount.

Cheers

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...

thanks RS2000 i'll give that a go aswell. charrett I didn't notice any abnormalitites in the cam, the motor has been completely reconditioned and i've only done about 3000kms on it so it seems unlikely, yes?

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

That sounds like an exhaust leak to me for sure.
 
Matt

exhaust leak +1 

All you have proved is that the noise is more audible when there is no exhaust leak due to loose header bolts.
Do yourself a favour and do what i suggested in my earlier post.
 
Cheers

If it is louder and more evident when you tighten up the extractors and sounds like a ticking sound that is more evident under throttle /load, it really sound like exhaust (pardon the pun)...  It could be a hairline crack in the extractors, that when you tighten them, it opens up more....  Or a dud extractor gasket that is leaking too...
 
The more an extractor is cracked, the worse the sound becomes and the engine also goes off song too... My race car broke #1 pipe on the extractors at Sandown 2 years ago, and in the distance of the main front straight, it went from sounding like a cracked header, to fully broken off and significantly down on power... Backed off and idled back to the pits... The pipe had broken off totally (100% around) and was about 5mm out of alignment....  Had to drive it home with a Coke can clamped around the extractor pipe and it sounded like a tractor and ran not much better than one.  Sounded like a cracked extractor, but 200 times worse..... They start off small, and sometimes un-noticed, but it will get worse till you can hear it idling and then feeling a power loss if you still do not fix it...

have you tyred pressurizing the the extractors and the exhaust system"  pump it up say to 30 PSI that should find any cracks -or holes -