I'm not sure how that would work to be honest. I did block all the ports bar one on the heat ex and then blew into it to see if its holed internally. It isn't.
Sort o Sort of next to the spark plugs holes, some new heads have them and they need blanking (approx 10mm diameter hole) will try to get a picture
They're actually where the m6 bolt would go to hold on the head tins either side of the inlet manifold!!
don't wish to sound trite, but I reckon it'll be something obvious that you've overlooked....head bolts torqued? head to manifold, manifold to exhaust or heat Xr...loose plug? loose baffle?
Obvious question but have you reported any if this back to the people who rebuilt it? Surely they will have bench tested it? My guess in order; HX to head it zorst. Head breather (though shouldn't be noisy) EGR hole. If its a new head it will have one which needs to be blocked. Head not mated to cylinders correctly. Either one of these issues should have either been spotted or pointed out to you by your 'professional' and he should be your first port of call before you do anything else.
I sincerely hope it is something simple I've missed so any suggestions are welcome. And don't worry about sounding like a trifle, I like trifle.
To be fair to the builder Zed and me thought it was our fitting of the heat ex which is nothing to do with the builder. I'll be talking to him on Monday and if it turns out that something is amiss from his work it will be corrected at no cost to myself. If I do have an egr hole in the head he will need to explain to me why he didn't blank it himself or even mention to me that it needed doing. Trust me I am not the sort of person to roll over and get stitched up, what I'm doing at the moment is a mixture of rectification/fault finding because I need to have a better idea of what's wrong before I start going in all guns blazing.
Ok I couldn't wait for daylight so I've just been out and checked. I do have that hole in my head........ And it has a shiny new blank in it. Ho Hum! So it's not that then.
That's the one!! @sANDYbAY if it looks like the above pic, that'll be the problem, as the holes go all the way down into the exhaust port, just behind the exhaust valve!!