timifakay:

The exhaust gas is already out of the engine, and having a catalyst is for safe disposal. Therefore, Catalyst is like a water closet/ sewage or septic tank, without catalyst is like "throwing shotput".

When d "septic" tank is clogged,what do u have ? Definitely a flow back !!!

Try changing your spark plugs(all of them),cus bad spark plugs can cause misfiring which can in turn cause vibrations. Also check the mounts(or seats as we call it) that hold the transmission in place.
Oh and yes,clogged catalyst converters can cause misfiring,reduce efficiency etcetera. Hope this helps.