After installing new cats I started getting a....

[ktown39]

...rough, bad-gas kind of sound from the front of my Ex.
If I put the engine in neutral and rev it I don't get the sound but if I'm in gear and get to around 25-30 M.P.H. it kind of sounds like a low rumble mixed with a missing or lifter type of sound. My CEL light does not come on and I can't tell it is causing any type of damage but it bugs the living hell out of me to hear and feel it. After getting up to 50 or so it seems to go away. My mechanic is stumped. Any suggestions as to what it is?

 

[unclemeat]

Did you change the oxygen sensors, and reset the computer?

 

[ktown39]

I reset the computer but did not change the oxygen sensors. Do you have to change them all? Or is there a way to pinpoint which one is bad?

 

[explr1]

Who makes them? Were they installed in reverse direction? Are they welded on or clamped? Clamps suck and do leak. Check everything for leaks and looseness.