Exhaust blowing and turbo losing boost

[travs]

Wonder if anyone can help - I've had a bit of a search and not found anything but if anyone can point me towards anything that would be cool.

Had a bit of a blow for a while when exhaust was cold but disappeared when warmed up - been told this was manifold.
Yesterday i noticed it was a little more evident - low rumble on idle and pulling away after warmed up. Today I noticed that the turbos are laggy and the boost gauge needle struggles from when reaching positive boost - in fact the needle twitches/flickers at zero and struggles to move up from here. Obviously I've only tried this a couple of times to see what's happening.
Car has been remapped and boost is capped at 16/17psi but I very rarely put my foot down, always warm up and cool down the car as much as possible.

Could anyone tell me what they think might be happening ie where to look first? Is this a common thing? Engine's done about 70k on original turbos. Bit of occasional police sirening but only really when cold.

Any help greatly appreciated.

[travs]

Also - continued to search but don't have the "classic" manifold rattle

[Trig]

Boost leak I would guess.
Pressure test it ASAP

[travs]

Thanks Trig, I'd assumed that sort of thing and will as soon as I can but as I'm not sure what link there is between the hot side and the cold side, could this be related or is it coincidental? ie I take it its nothing to do with the classic TBB, F-Hose, Spider Hose etc. etc but that's the cold side right? the exhaust is the hot side?
Or am I completely wrong? I appreciate there is only so much I can get in a response without someone looking at the car - I'm just looking for what's the most likely culprits to look for based on people's knowledge and experience