Today when I pulled into my garage, I noticed a slight burning smell and heard a sizzling noise. I looked underneath my car and it looked like it was coming from one of the catalytic converters. It was raining heavily today, so I'm guessing that has something to do with it, but should the cat be so hot that water would do that? Both cats were replaced less than a year ago under 80/8 warranty.

 

Your exhaust will get hot enough to boil water easily. Ever gone through a puddle and seen the massive steam cloud behind you(maybe not in the audi but trucks do it a lot)? The noise could also be from water turning into steam or the metal cooling off and shrinking just a little. It should be easy to see if there is anything stuck on the exhaust that would burn or melt. What you described isn't that hard to figure out, go look and see whats there.

 

Ill have to take some pics of my cat after a few WOTs its red hot egt's are very hot.

 

A cat'll glowona 1.8T after some WOTs. Being that your 2.8 isn't turboed, they shouldn't get hot enough to glow, but they'll still get some Serious heat built up.