exhaust tick
 

i recently picked up a 97 jetta free, needed a downpipe, so i pulled the manifold off and pulled it all in one piece to avoid breaking studs (live in maine very rusty)
got a new downpipe all new gaskets, and a tick that sounds like a manifold gasket or cracked manifold; if this was there before i could/didn't hear it. it only does it a low rpm under load or when you first step on the throttle. car isn't on the road yet and needs both o2 sensors replaced, it has a horrid misfire at idle, and before i tear it back apart to look for a lead i can't see or feel im curious if anyones had problems with these doing that. or is it maybe pinging/spark knock from needing a tune up and 02 sensrs?
i appreciate any help!