Strange exhaust note near cat, one tail smokey, one wet

So then. Recently my 99 GT with flowmaster aftercats (not sure if the system was done full, it was done before I bought the car) has started making strange noises near the cat.

At idle, and worse with throttle there's a loud ticking/strange exhaust note coming from near the cats. *MAINLY* from the passenger side. It sounds like a harley exhaust, but from the middle of my car.

The tailpipes are both putting out normal noise/heat.

This is while cold:The driver side pipe was putting out a white smoke that smelled a little musty. Like a dryer vent from a house might smell. The passenger side pipe had no smoke. But it was putting out some moisture onto the ground.

It just recently started raining around here. Not sure if problem is connected.

I'm going to take it into Midas since they will check for exhaust leaks (and I dont have a lift) but any ideas to try in the mean time to tell if it's a leak or something else?

Thanks!

I took it out for a drive.

In all gears, when I first put throttle on, the sound (which is like an old VWbug, a quick rattling) is very noticeable. The sound stops after i leave the throttle on for a little.

In 5th gear the sound is very noticable around 2000rpms. It doesnt stop.