Took my greddy header of my si and put the stock one back on becasue im selling it. When i drive it has a kind of clicking sound coming from the header but a little softer. Went back under my car, retightened everything and still the same noise, sounds like a lawn mower. Jacked it up a third time and there is a little air coming from between the end of the stock header and the cat. I replaced the gasket between the exhaust manifold and the engine. Does the area between the cat and end of header need a gasket also....please help....my cars jacked up in the garage right now.....

 

Yes, you need a gasket at all joints in your exhaust.

 

alright,,,,thank you...is that what is most likely causing the noise?
since your in orange county you should come over and help j/k