Hi everyone. I'm new here and have an oddity of a question. My wife has a 1993 Club Wagon (no seats) and had the catalytic converter replaced about a year ago. Its her landscaping rig. She just mentioned this odd loud sound that's occurred since the cat install. OMG, sounds like an air bypass valve or something. Very loud when warmed up. So I go exploring under the van and find (what I think are) the lines from pump to the cat have been cut and plugged. It's probably a non stock cat. I'm guessing that the air pump is pumping its little heart out and the air has nowhere to go! Then when the motor is revved up or under load, the air escapes out some valve. Am I right?? I don't want to remove the pump, and I was thinking of just unplugging the lines and let the air escape under the truck. Do you think I'm on the right track to quiet down an old work truck? BTW, the shop that did the cat is out of business. Thanks!