I have a 2014 Evo X that I picked up in September of 2018 that came with a down pipe, high flow cat test pipe, and stock cat back. Within a week of having the car I put the ETS V2 Extreme catback on and man that car was loud. The old down pipe and high flow cat test pipe setup is from an unknown manufacturer. I'm not sure if the previous owner had it custom made, but there was v band flanges where the down pipe and test pipe meet. This meant the old setup had to go and I went with an ETS recirculated down pipe with an Ultimate Racing mini muffler test pipe. The removal of the down pipe went smooth expect for the very top bolt. I have a feeling the previous owner cross threaded this into the turbo housing. PB blaster and a torch were not able to save this bolt so I had to drill it out. The tone of the exhaust changed drastically. With the mini muffler the exhaust note is much softer, and the highway driving is much more bearable. I do miss the aggressive exhaust note with the high flow cat so I might order the ETS high flow cat test pipe in the future for when I get bored of the much quieter exhaust. I'm sure my neighbors appreciate my car being substantially quieter now. The numbers may not appear to be very different between the HFC and mini muffler, but there is a huge sound level difference in these results. Overall the car is much quieter in every aspect of driving. I took some measurements of the old setup versus the new setup with a sound level meter.

HFC:
99db cold start (outside car)
84db shifting at 3000 rpm accelerating (interior)
76db cruising at 2000 rpm (interior)
80 to 82db cruising 75mph 3500 rpm (interior)

Mini muffler:
96db cold start (outside car)
82 to 83db shifting at 3000 rpm accelerating (interior)
70 to 71db cruising at 2000 rpm (interior)
75 to 76db cruising 75mph 3500 rpm (interior)

 

Excellent first post. Thanks and welcome!