Fiber like material from exhaust
I took my car for a Highway drive after parking it for few weeks in the parking lot. When I started to drive, there was a variation of sound while reving in the cabin. And I also drove in bit high rpm’s than usual, but later I found out a fiber like material from the exhaust tip. When I asked the mechanic, he told that it’s usual that some people place some kind of stuff somewhere in the exhaust after removing catalytic converter to reduce the sound and it came out after I drove it in high rpms. Is that true ? And still the car doesn’t sound like how it used to sound before. But the sound seems to be rough only while driving. While idling, the sound seems to be okay. Any idea what it is and what I could do to fix it. It’s a w203 facelift (2005) 2.2 diesel.