I had a problem from day 1 with an '06 Civic. I put up with it for almost exactly 2 years before I brought it in for warranty repair.
It sounded to me like an exhaust component that was too close to a frame member, or something -- I'd get that exhaust howl (growl) at low r.p.m.'s, with the intensity varying with engine speed. It was especially loud at around 41 m.p.h. in high gear (AT).
The shop looked up the TSB and performed the fix, which involves installing a longer drive belt (serpentine) and rerouting it. It has nothing to do with exhaust.
I wonder how this works. I'd like to see a diagram of the fix (TSB
06-059). If it can be 'rerouted', that would almost have to mean that one or more components is rotating the opposite direction. Interesting.It seems to have fixed the problem, and the car is much quieter while waiting at red lights. I've heard that the noise can return, so we'll see.