2008 a4 1.8tfsi ticking noise
 

Hi guys hopefully someone can help me with this.
Car had 90000 miles and timing chain done within the last 5000. Oil was changed 500 miles ago and I recently noticed a ticking coming from the right top side of the engine along with a small missfire which came back as being no 3 and 4 on a diagnostic. When we put a stethoscope on the manifold cylinder 1-3 sounded the same and no 4 had the clicking noise. Could this be an injector issue or lifters ?
I had ordered a new injector for 4 put when my mechanic went to fit it he damaged the seals on 2 and 2 so now am waiting on 3 more injectors