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.