So I swapped out and sold the MBRP XP catback system, as the "Boom" was a bit more than I wanted. The Mountune is now installed, and I'm about 80% satisfied (which is pretty good for me). However, I'm noticing a sound at boost that I've never heard before and I'm not sure if it's just normal spooling. Performance seems fine, but when at boost I hear a rolling/mechanical type sound. I didn't notice this when stock, but when stock I had the SS still installed. After the MBRP went in the SS went out. The MBRP was pretty "Boomy" so I would have had a hard time hearing any spool sounds. This is the first turbocharged vehicle that I've ever owned, or have any experience with. I looked around Youtube for spool sound videos. Most of these had turbos that made more whiny sound. So I'm hearing this more mechanical/rolling sound, am I nuts, a dolt, or both, or is this perfectly normal. I did replace the stock BPV with the Mountune BPV a while back, could that have changed the spool sound, perhaps when venting back to the system???