Blowing exhaust manifold?

very very common this on the 18xe and 20xev, on veccy or cav,tell tale is loud clicking on cold startup that gets quieter the more warm it gets..unless really bad.
normally its the left side (stood at front of car) of the manifold that is blowing due to excess heat build up and it has warped and thus caused the studs on that end to break.
if not this they also love to crack across the top underneath the heat shield.
so firstly u need to check how bad and whats involved.
take the heatshield off by undoing the four torx 10 bolts.
a bit of manipulaton and she will come out, u may have to remove the engine hoist bracket or the coolant pipe bolts above if your struggling.
now look for black sooty deposits..a crack will be obvious....if it is merely cracked a cheap effective repair is to simply weld it in situ, i have known these to last for ages.
now the most common, examine the left side of manifold...is it black at the gasket joint...if it is, your warped and blowing. if bad it will have broken the bottom lowest corner stud, or worse the above one also...if you are going to take on the task yourself get a 13mm socket on these two studs and carefully try to undo....if go tight, wind back in, and out, lubing as u go. tenner says they feel loose and u think they'll come out, in fact they are normally already sheared in the head and merely fall out when u try to undo.
at least now u know and can drive it short term. and get the bits needed
to repair this some garages remove the cylinder head to drill and retap, some drill out in situ.
it is poss to do in situ, and do well if your competent.
to do...and remove the manilfold...
remove heatshield, remove, pipework above,
remove the egr pipe off of manifold,
undo breather pipe from cam cover and undo two 13mm bolts and remove full pipe to crankcase. bung hole up with tissue!!
undo two bolts under egr valve gubbins and move the obstructing part out of way.
undo the four bolts for front pipe from underneath.
whilst under here undo the 15mm lower power steerin pump bolt.
up top get 15mm spanner, undo and remove multi v belt, undo upeer two 15mm power steering pump bolts.
the dipstick also wants to be removed, simply undo bolt to pump and twist and pull. the pump can now be movered and lowered out of way
undo and remove two bolts and remove thermostat housing. place out of way.
undo all remaining maiflod nuts, studs and remove manifold.
bung all holes in head etc with tissue.

now u can start to repair. get a small drill centre punch the broken studs, now pilot drill out straight and in line with head etc...
BE WARNED U GET THIS WRONG U DRILL IN TO HEAD AND WILL HIT WATER JACKET!
so long as u take your time and just keep checking, your ok. when u go throo stud, there is normally gap at rear of it, so drill will go free suddenly, stop now!!!
build up with drill bit sizes till your not far off of thread...
when happy, get a suitably sized "easy out" (these are fab) and twist in and undo till it pulls remains out.
alternatively, get well close to thread of stud, and very carefully tap out so u get to old thread.
once you have done this u can feel well smug and have five, lol

now remove all remaining studs with stud remover, or two 13mm nuts clamped together on studs and undo
fit all new studs...and nuts...i strongly advise a new manifold but they arent cheap...so its upto, u a straight edge will tell u how warped it is.
clean up all surfaces..and rebuild back as u stripped.

just make sure no foreign bits in manifold to head port holes and breathe rhole, also clean this out, use new gaskets throo out, no bloody paste! new studs! and u Will need a new thermostat seal on rebuild, and of course anti freeze etc .