Strange rattling under car
 

A week or so ago, I had the catalytic converters on my car (Magnaflow hi-flow) re-welded, because there was a leak in the weld.

Ever since this, upon startup, if my car is cold (65 degree weather at least) and ONLY if the exhaust is cold it seems... I will start the car and there is a quick vibration rattle metallic kind of buzzing noise that comes from underneath the shifter (right where those cats are it seems) now....

I just got under my car, and had my brother start the car for me and OF COURSE... the rattling didn't happen. I then inspected the catalytic converters. It seems that the passdenger side cat has a slightly loose top shield (there is a metal and metal gap) and the other one on the driver's side does not.

Do you think I have answered my question? And is there any way to tighten this yourself?

Eh? Come on guys, nobody?