loud valve knock
 

i was on here a while ago probably about a year and reading some threads on people having a very loud knock coming from their head, i now have the same noise it is extremely loud and i was wondering if anyone ever found out what it was
http://www.youtube.com/watch?v=93hEYr-V4jQ
heres a video that was posted mine is doing the same thing
any help is appreciated i just dont wann tear into this before i have an idea of what it is
I know its not a rod because its at 1/2 engine speed so its definately valve noise i just dont know if its a broken spring or if its a sticky valve smacking wierd or what

I have a similar noise coming from my 1jz it's not quite as loud but just as annoying don't know what it is.

i found my noise not saying yours is the same but i have a bad head. before i bolted it to the block it sat outside for a few months and the cam bearings got rusted but when i felt the cams they spun fine after running for about 5 minutes the cam bearings were completely gone and now i have a "cam knock"