welcome to the world or rs turbos, lol , thats just the way they are mate but oce you get the niggles sorted out you'll be wondering what all the fuss was about,
sounds like either misfiring or mis timed, or stuck valves letting fuel ir mix ignite in manifold, maybe someone with more experince will have better answer ,
might be worth taking it to garage for straight answer , might be more money out in short term but saves chasing around for the problem