Was wondering if the after market exhausts, have the same large bend in the pipe underneath the passenger seat, driver's side? Seems unnecessary but I am wondering if GM was trying to "tune" the exhaust note by lengthening the pipe? Longer pipe will attenuate the higher frequencies.

 

High frequencies get attenuated by lossy material, such as steel or ceramic wool, not smooth pipe. Pipe length will determine the primary resonance frequency in the lower range.