when i drive normal (not too much boost) everything sounds fine, nice little roar from turbo. the minute i give it some welly the turbo goes from a little roar to a loud rough something not quite right sound. boost gauge still ok, 7 eights of gauge.
no rattles or grinding.

any ideas :unsure:

does it feel any different? when was the last time you changed the oil? if the oil was changed regularly, if might be the seals. do you see any oil that has dripped down under the car? since you are under there, check and see if there is any oil coating the bottom of the car. any oil loss? do you check?

have a leak from bottom of oil dip stick, changed rubber seal which stopped the dripping oil but it still leaks just not as bad - you thinking oil starvation!

possbily, or oil coking. it might just be the seals in the turbo that have gone. turbos also need rebuilds eventually. if poss, check out and see if there is oil under the car. check levels, etc. at least that will be several things checked off the list of possibles.

It could very well be the seals.

Sometimes, if the spindle rod is bent, it can also cause a loud whirring sound. The actual sound of metal grinding may not be obvious, then the pedal is pressed, though..

I suggest you do a thorough check.