Issue with my Audi A6

Hello,

I am a new owner of a pre owned 2016 Audi A6 2.0T Quattro Premium Plus with ~25,500 miles on it.

The car doesn't seem to have any major issues at all but when I cold start it or am in idle, there seems to be a very subtle vibration for 2 seconds every 30 seconds or so. When I cold start it it's very noticeable at the start and gets more subtle. It's a very subtle and gentle but noticeable vibration. No check lights or error codes.

I thought it might be because of some gunk in the gas tank since the car sat in a parking lot for a long time before being purchased. And having added fuel additive and now almost running a full tank of it, the vibration doesn't seem to go away. Does anyone have had experience with this issue or have any idea? My friends thinks it might be the throttle?

Please let me know your thoughts.

Thanks!!!