I just went from Akra rear section to full evo and noticed that you hear much more intake sound that can sound like a loud hiss when you first hear it. Much freer "breathing" setup that seems to amplify the intake noise. I checked my clamps again after a couple of weeks to make sure everything was tight and found no issues.
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18