2015 5.3 Chevy Silverado new Flowmaster Flow FX install - Terrible

FINAL UPDATE: Cut the muffler off and am running open exhaust. It's a tad louder than I like, but still not near as loud as open exhaust was 20 years ago on a truck.
Update: Holley replied with “no question” to my email explaining the issue. The question I had was implied with me explaining the raspy popping , unless that’s fucking normal for these mufflers. Terrible customer service. I am just going to trash the muffler and go with dynomax. I swear on everything holy I’ll never purchase another flowmaster or holley product. Nor will I ever recommend them to anyone else.
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New install, just muffler swap from factory muffler. No exhaust leaks I can locate. Sounds awful. From the cab it sounds the same as stock. Super quiet. Which isn’t exactly what I was wanting. Outside it sounds like raspy popping and barely louder than factory. Contacted Holley, parent company of flowmaster, and they haven’t emailed me back in a week. Not sure if I’ve somehow messed up a simple muffler swap, or if the muffler is defective. Can’t get flowmaster to reply.

[@ptcustom81]

I just had a muffler shop install a dual out Flowmaster Flowfx yesterday and it sounds clean and deep. Noticeably louder than stock. I also had them remove the 3rd cat while they was at it. Not sure why yours was so raspy.

[@TheSlugJones]

Me neither, man. I usually love and have no issues with flowmaster products. I used them in my mustangs in the past and they’re great. However, leaving the rest of the exhaust stock and just cutting off the mufflers seemed to satisfy me. Not too loud or obnoxious, not terrible drone. I’d rather have had a bit quieter with more deepness, but it worked out.

[@Dnasty1]

@@TheSlugJones Did you ever get the sorted? It sounds a lot like scavenging and possibly a leak somewhere. Maybe they didn't do a good installation? Or there could be something wrong with the internals of the muffler.