Just getting my new motor 347 stroker, all sorted out and have been driving my 65 Fastback and it was running great. I fixed a header leak and all was well. Now the car fires right up but there is a slight vibration that is RPM related. It's worse or more noticable at lower RPM's; you can also "hear the vibration" in the exhaust if you know what I mean. I know there are alot of things that could cause an engine vibration but everything was good and I haven't changed anything. Any ideas would be greatly appreciated.