All the new standard ISTA firmware updates removes most, if not all, exhaust burbles in all N55's as to give more exclusivity to those willing to shell out the extra coin for the PPK update. My 135i was a throaty muscle car gurgler for most of it's life until the PPK STG1 was released and they subsequently re-fashed my car...burbles gone and throttle response softened. This is all part of the master plan. My new 335i F30 currently has the burbles as well, although not as raw and raspy due to all the exhaust plumbing vs. my 135i but I am sure once the PPK is released they will zap it. How shiity is that?
M235i F22: Prem.Tech.+
335 F30 MSport: Prem.Tech.NAV.+
X-335 E92: Prem.Sport.+
Audi A3: FBO.