Chain kind of Sounds when accelerating. Not a turbo nor timing chain

Hi When I press the accelerator while neutral after 1*5 rpm it sounds some kind of chain sound coming Near engine. While running if I accelerate and crosses 1*5 and above it sounds like a chain but below 1*5 RPM it’s doesn’t sound anymore and goes smoothly. I checked it with mechanic and Audi showroom. One told it’s not a big issue we have to change the connector to the engine for not getting that sound. Another told he is clueless and cannot say anything.

How to get rid of that sound ?