The flexplate from a atx car would be a challenge to mount a clutch to But yeah I used the alignment tool, the proper axle. Vibrations, as previously noted, are often hard to diagnose because they can be amplified and sound like they are coming from somewhere else then where they are actually coming from. The part that makes me think it could be the cat is the lack of any evidence of something actually hitting something and the fact that I got a catalyist effeciency below threshold code that I never had before this problem. If memory serves me correctly the car didn't make any noises when I first test drove it after the swap but started making the noises on my way home from my parents place.

 

Yeah, I don't imagine you could have used the A/T flexplate without noticing it. But you DID use the longer bolts for the flywheel, right?

Since a new cat is pricey, it might be worth it to unbolt the exhaust so you can shake the cat by itself. Maybe it's just me, but I'd want some confirmation before I spent that much money.

 

Yeah I agree I don't want to spend the money unless I know for sure its the problem. Replacing the atx rear mount and bracket for the mtx one wasn't a waste of money, only $40, and just makes the swap more complete. Yes I used the longer flywheel bolts. I actually got all the bolts necessary for the swap from a donor car in the wrecking yard. Car drives fine and runs fine. Mileage even seems good. I am feeling lazy today and don't really want to bother with the cat but we will see.

 

Yeah, I completely agree with that.

Still, the noise would probably drive me nuts until I figured it out.

 

and it does

 

Hey if the cat is the problem what do you guys think of this?
http://cgi.ebay.com/ebaymotors/Heade...%3A1|72%3A1171

 

FOUND IT!!! OK so on the driver's side engine mount there is a mount movement limit in place to prevent excessive engine movement if the mount were to break. Well what was happening is the cat would start to plug up as it would heat up and therefore cause the engine to strain harder at idle causing a heavier vibration. This would in turn make the mount continuously hit the limiting bracket. Thats also why I got the catalyst below efficiency code. So to fix the problem I simply replaced the cat with a section of pipe and used the defouler trick to prevent a CEL. The car isn't any louder that I can tell but does have a significant gain in power. And of course the banging noise is gone