I will tell you something that maybe sounds funny but remove your belts and run it for few seconds to see if the noise is present.
I had an at about the same noise coming from the head and was louder near the idle valve. Was sound like a valve with too much clearence if you know what i mean.
I was searching for days as it was very stange and had spent a lot of money to this engine..to find out that was a faulty altenator bearing. But the sound was like it was coming from the midle of the head.
Give it a try.. Also same noise can be produced from oil deep stick mount if not tight,crank pulley if not tight enough,water pump and tensioners of timing belt. Have a look at them aswell.
Chris