1.5 petrol turbo issue?

Hi

I recently bought a 2021 Kodiaq SE L 1.5 with 25k on the clock. 

But something just doesn’t sound right…. Under acceleration there’s a tapping noise coming from the engine audible within the car. I’ve taken it back to the garage and they have the engine the all clear….. however I keep driving it and it just sounds … too noisy. Noisier than a car I test drive. Unfortunately I didn’t test drive this car for long the morning I bought it as a family member had a stroke and I needed to get to the hospital!

At first I wondered if it could be spark plugs or the injectors, but I’m now thinking perhaps the turbo as it’s not constant but just starts just start I start accelerating. 

Has anyone experienced similar at all? I’m not sure if it’s related but mpg seems lower than expected also. High 20s for typical local driving (average 40 zones) and 39 for a longer motorway and a road journey I just did. 

Thanks for any advice.