Loud engine and smoke before turbo engages

After shifting into a new gear or slowing down below 2,000 rpm, as I get to the 2,000 rpm mark the engine makes a very very loud noise that sounds like a diesel but far too loud, a lot more smoke is emitted from the muffler. Don't notice a decrease in power or anything like that and as soon as I hit about 2300 rpm the turbo engages and the engine again sounds normal. I ran a scanner on it and it came back with p0401 and p0103, mass air flow and exhaust gas recirculation flow low.

Any idea I'd one of those issues could be the culprit or would it be turbo or something else? Thanks in advance