Blown turbo? Popped pipe? Popped intake seal? Dumb valve open?

[Howstar]

Scene;
Driving on motorway at fd motorway speeds, 70% throttle, and \'pop\' like a back fire pop and turbo pressure drops down from 0.9bar max to 0.4bar and won\'t go any higher.
Also with loud whistling/hissing sound from turbo/dump valve area of engine whenever in +ve pressure
First thought was that turbos has gone bang, so limped it home.
 
 
Confusion;
Been out for couple of short drives since.
- Car idles like normal 0.9k - 1k rpm no problem
- Pulls away no problem
- Drives no problem
- No smoke at all from exhaust (straight thru)
- No bad smells
- No oil leaking
- Oil level not gone down at all
 
Only difference is can only get 0.4bar out of turbos, loud whistling/hissing sound and no dump valve.
 
All things lead to popped pipe in my opinion, no obvious pipes have come off but i need to check properly.
Just wanted outside opinions and recommendations from proper rotary guys.
 
 
Running;
Apexi intake,
HKS twin turbo pack (sequential)
HKS dump valve
Mapped to 0.9bar boost max

[marf]

Start with the basics, remove and refit all the intake pipework from the turbo to the throttle body.