where are you located bro? u have the rhd s13 right? see me and sean have been told it could me a lifter, it could be this thing that needs to be replaces (cant think right now), or it could be a very very slight knock. u can seriously barely hear it. when i thru a rod b4 it was sooooo loud. u could hear it clearly from 20ft away. so idk. id like to get about 1k for this. and if i can determine wether it is in fact a knock or not the price my change. but thats y im testing waters! lol so keep thowing shit at me!