opcorn:
I don't think I can help beyond the obvious.
What brand of cat-back? A cheap painted one (or even a cheap 'stainless' one) could produce smoke as paint, shellac and/or 'cosmoline' burned off.
Yes, removing a catalytic converter 'could' possibly unmask visible oil smoke (in theory). The job of a cat is to burn up unburned hydrocarbons (and they shouldn't be removed just because you can get away with it... they aren't there for decoration. /rant).
Watch your oil consumption. Document loss (miles per quart).
How many miles on the car? How long have you owned it?
