My car has been well noise-insulated, but gradually and slowly getting louder. In particularly around 2250 to 2750 rpm the exhaust is beginning to roar like a trumpet. This condition is worsening over time, and indicates probably the glass wool or whatever stuffing inside the muffler is deteriorating or disintegrating. A resonance develops. The outside of the exhaust has no holes or anything.
Does anybody recall similar problems?