New problem

So I was driving through derby last night and really starting to enjoy the car, I went round a sharp corner and as I only had a quarter of a tank I got fuel starvation (this is probably totally unrelated but thought I'd drop it in there) the usual momentary pops and bangs happened (for like a split second)
Any way, probably 5 minutes after that I felt a slight hesitation, I thought nothing of it.....then again.....then I noticed my afr readings were going very VERY LEAN and well into the red and the car hesitating even more...got to the girlfriends house switched it off,grabbed her and some pressies and got back in the car to make the return journey home,on any thing other than a very VERY LIGHT throttle its hesitating and the afrs are extremely high again......then all of a sudden a noise starts to develop,it sounds like a firework being set off without the bang at the end, a very loud whistle/wining noise. At this point I turned round and went back to the gfs house and left the car there.
I'm thinking perhaps a boost leak? But would that not cause it to run very rich? When I've blown pipes off before it's blatantly obvious and the car comes to a stop, I've not had chance to have a good luck yet but there was nothing obvious (literally had a look for 30 seconds).
So... thoughts,ideas,things to check etc?
Won't be getting the car back until tomorrow now.

Boost leak
What you got fuel pump wise ? Could it of come loose on cornering hence lean and pipe off it and that the funny noise or is noise from engine bay ?

Get yourself one of those....
http://www.ebay.co.uk/itm/VS2030-Sealey-Tools-Turbo-System-Leakage-Tester-Engine-Leak-Detection-Kits-/311669115717?hash=item4890ed4b45:g:rBwAAOSwExJXog95

I've been fighting with boost leak lately, it would run lumpy as hell on tick over when you'd floor it it was sounding like machine gun was fired... What confused me it had high lift cams so I've thought that was cause of lumpy idle. But like you've said you'd expect it to run lean on tick over and very rich on boost. Another thing I've come across (you might have two faults sometimes) was exhaust manifold leak, wide band didn't have enough exhaust gas to measure and it was showing lean.