Header rattle/ catalytic converter

Hey guys, i had time to install my dc sports headers. it was pretty simple and didnt take long, but when i finished up and started the car, it sounded fine, but when i drove it around, this really nasty rattling sound is heard, and its in the header area also. im pretty sure i tightened EVERYTHING, i even made sure to tighten the other exhaust bolts. any ideas or experiences?

Also, about the catalytic converter, is it bad for water to enter the converter? When i was doing the headers, the old ones were hot, but not just off the engine hot, so i decided to cool it off by spraying water, but i took the O2 sensor off, and some water got in the downpipe (which i found out when i got it off *tastes nasty*) . I thought i'd be okay since the exhaust heat would dry it all up.