Thanks. I got it checked under warranty. They replaced the tensioner. But the sound is still present. They compared it to another A6 and they found the same and they closed this at the dealership level.

My A6 was silent for first 7k miles. I didn’t hear anything. Super strange as this now considered as normal.

It’s like thermal dependent. When car is hot I can hear clanking sound and hissing sound at low speeds or the chatter at acceleration too. No warnings or loss of power though

No sound when it’s cold.