AWX occasional limp mode & noisy under boost

[JayB5UK]

As per title really, my old girl has done 160k now - I have owned since about 130k and she has always pulled really well.
I've got no black smoke that I can see, no real drop in mpg, but she is sometimes dropping off into limp mode, most times when the car is pretty cold from work, but I have to moderately accelerate down a slip road onto a dual carriageway 1/2 mile after strating my journey.

Other times booting it when warm up hill etc will do it, but usually when she is fully warm it won't do it.

However, all the time, when you give it a full boot at between 2 & 3k rpm, it makes a right old racket - rushing air / flapping and then when you change gear, it sounds like it's got a funny wastegate or dumpvavle noise.
If you use less right foot, the noise is less so, which makes me convinced it is post compressor side of the turbo?
Do the PD TDis have a diverter valve - or is there a common obvious place to check for a split hose / elbow?

I did change my EGR valve for another used one about a year ago, didn't use a new gasket at the time, but it sounds as if it is coming from further away than that, but I could be wrong.