Long tubes through cats will be QUIETER then manifolds through cats. Reason being, is that manifolds allow much more erratic exhaust pulses, which reverberate throughout the manifold and increase noise, while a long tube smooths and evens out the tone.

HOWEVER, the opposite is also true. Longtubes through NO cats will be LOUDER then manifolds through no cats, because the long tubes allow for much more peak flow. At any rate, I'd stick with 3" pipe completely. Looks like you got a hack job