P12 2.2 Dci whooshing noise

We have a 54 plate P12 2.2 Dci estate,138000 miles,owned 6/7 years and has been a reliable workhorse covering 60K plus miles.
My wife noticed a whooshing noise and I decided to investigate.Car drives fine but noticed black smoke on revving/acceleration,possibly turbo showing early signs of failure??I took the turbo pipe work and housing off,attempted complete removal,managed to get egr pipe off,exhaust manifold partly off,but stud/bolt at back of manifold where it attaches to turbo very hard to get at.I had to heat bolts to remove them and already spent a few afternoons trying to remove,emptied coolant,drained engine oil (with difficulty as oil was cold) but realised inside of turbo had no play,it span fine so bearing must be ok??Best bet was the oil had gotten dirty,black,sludgy,so new oil and filter may help (6000 miles since last oil change anyway).
Last year or two car has experienced going into "limp home mode" if revved too hard over 3000/3500 rpm but after pulling over and restarting seemed fine again,also when cold runs uneven,"hunting" at low rpm,better when warm.
Conclusion now was suction control valve playing up,not the turbo.Bought a new Denso valve and managed to replace in an afternoon,you have to remove windscreen wipers (used a gear puller) and the motor,plastic bits,metal shield etc to even see the SCV.Its hard to get at on the Dci,offside of engine at back under oil pipes/fuel pipes and electric cable but not impossible.I had to get up and kneel in the engine bay with allen key to make the swap.I had left battery disconnected for over 90 mins during this time so thought it would just fire up and run ok (this forum has quotes of 90 mins plus as long enough for ECU to reset when disconnected from battery and no need to do reset procedure for fuel pump),failed to start repeatedly.
Tried the Fuel pump reset procedure,complicated sequence of waiting several seconds,"on and off" accelerator pedal etc,tried a few attempts with nothing happening,the key was to get EML flashing,this means ECU in learning mode,but still no luck,car would not start.Managed to get EML flashing a third time and car started,ran for a few secs and died.Blown 140A relay,battery relay in small fuse box left of battery.
Nissan do not stock these relays,they wanted me to wait 3 weeks and charge £19!Found relay offered on a well known auction website for £1.70 each,£2.45 with delivery so now waiting for new relay (ordered two just in case).
Car alarm works,sat nav screen ok,radio ok but ignition,dash and central locking not working with blown relay.
Any ideas whats going on????Why would the relay blow???
I thought I may as well change fuel filter while I have access to it,under £9 from my local GSF parts supplier,I will fit filter after getting it running.
Imagine main Nissan dealer trying to do all this work,they would charge a fortune to diagnose and get running again and if they blew a 120A battery fuse I would be without a car for almost a month,just not worth the bother for our old banger.
Our car has full Nissan service history up to 90,000,until we had an airbag light on and our local Nissan dealer wanted over £2K to replace all the airbag wiring,sensors etc.
I found out how to reset airbag for nothing!Four/five years on and now rarely ever see airbag light come on after I disabled the passenger electric seat,moving it about or messing with the glove box seemed to trigger airbag warning light problem (glove box permanently locked!!).
I just regularly change oil and filter myself,once per year/every 10,000 miles seems ok.Local garage takes care of brake discs and pads if I haven't the time to do it myself,saved a fortune on main dealer charges.
Am I on the right track?
Any advice welcome

Thanks for the tip but checked pipe work and all seems well,no splits or damage.Maybe whooshing noise was noticed because radio was off and my wife made me worry about it,turbos do make a bit of noise,a few years ago I had a 1995 R33 GTR and 94 Pulsar GTiR and they were very noisey!!

 you seem to be doing well, the noise you describe would suggest a split pipe or loose connection these turbos are not generally noisy. If it is a whirring noise going up and down with velocity then that would suggest turbo bearing failure with the vane rubbing on the casing but you state you have checked that and it is steady as a rock.

It is on the underside of the fuel filter, just a couple of presses should make it good and firm

Water in where it goes?