Not really...my car flows great and its quiet until WOT.
I have Catless Pacesetters, 3" Custom piping from the catback flange back with Flowmaster 40's and a stock GM Resonator. No drone or rasp here.
both will eliminate drone, however, they are different in their application.
glasspack: does its job to 'smooth' out the exhaust note, but doesn't really provide any sound dampening.
resonator: used to make the exhaust quiet and helps keep it from being raspy.
I don't think the OP's exhaust has no resonator. Having the stock resonator in place definitely helps. You did it the way that I would've. What piping did you use?
would it make sense to do a glasspack and a resonator in line? so you get both the benifits?
I also have the SLP cat-back along with SSAC headers, same as speed daddy, and the drone is annoying. I bought a magnaflow resonator 3in in and out for like 80 bucks. I'm getting it installed monday and i'll let you know how it sounds.
Alright here it is, before.... skip the video to 3:10.....raspier than crap
YouTube - Lightly Modded GTP Walk Around
and after, smooooooth
0623102055-00.mp4 video by suprasrock88 - Photobucket