Ticking/Knocking/Hissing
 

I have a noise comming from my engine. When sitting in the dirver seat it seems like it is comming from the center or the right side of the engine.

I have briefly pulled the vanity cover off of the top end and then it sounds like it is comming directly from the top of the engine or somewhere towards the back.

This is a ticking/hissing sound and it sounds like somesort or vacuum/exhaust leak but i am not sure. The noise will speed up and slow down with the RPMs and after the engine is warmed up it seems to go away.

It is not very noticable but i tend to notice eerything. The car is a 2008 mazda3 i touring with about 108K miles.

I am thinking its a leak in the header gasket or somewhere along the down pipe. The more i do reading i am hearing about noisy lifters and injectors but my Ram SRT10 has the noiseiest valve train i ahve ever heard so i am realitivel certain that is is not that. Any help would be appreciated and if its a headgasket how diffucult would that be for a bac k yard fix.