It's almost definitely the turbo, as said remove pipe between airbox and turbo, with engine stopped see if you can detect any play in the shaft that runs through the middle of the turbo, the one with the fan type wheel on it, lift up/down, try and move in and out, a tiny amount of up/down is normal, but any in/out movement is bad news.
There are no seals as such either end, so renewal or rebuild time, but not too bad price wise on these.
Not sure which make you have but suspect it is a KKK, the turbo repair places will know right away.
I use the turbo centre, 01924 404112, ask for andy or craig, they do a pick up and delivery service as well, may have one on shelf, or may just suggest having your one rebuilt.
tabetha