Big-end shell going shouldn't affect compression or emit smoke .. it will manifest itself as a knocking/rumbling sound which gets louder as you rev and as the oil warms up and thins.
If it's a tapping sound, it's not likely to be the big-end .. it's more likely to be top end. Not familiar with a diesel engine and how it's constructed, but it's possibly the cam or rocker related. Don't think it uses hydraulic cam followers (or does it?). Might be the little end (piston pin end of conrod).
Have you tried the old mechanics trick of placing a long screwdriver or metal bar against the engine and pressing your ear against the handle/end? Move the screwdriver around on the engine until the noise transmitted through the screwdriver is loudest. Or even a stethoscope if you can get hold of one!
On most cars, the big end going will make it loose compression (Albeit only a little until it really does go) and on a diesel, should produce a fair bit of smoke because of the lesser compression. I think it has hydraulic cam followers, but I don't know this engine at all yet, so maybe not.
Haven't tried that trick yet, one of my favourites too, but I haven't even had the plastic top cover off the engine just yet, I will be doing. I'll be disconnecting the injector plugs one at a time too, see if the noise continues or goes away. I might do that tonight if I get time and can brave the cold long enough.
I have a nasty feeling it really is bottom end related, the guy at Auto Lusso reckons the big ends are the most common to go on this engine, but will just have to do some more diagnosis and find out. Think tonight will be injector plug removal and the screwdriver test, shoot out to Halfrauds and pick up some more flush, oil and filter then on Saturday I think I'm going to do the flush again and if the problem still isn't solved, I'll pull the sump off to confirm bottom end.
I did see a piece of shiny metal in the oil pan when I did the last change, but I had to muller the sump plug to get it off for one thing and for another we only just broke a car for parts a few weeks back, so there are plenty of shards around the garage, could have been from either tbh. Guess I'll do some more testing and come back to you all, lol.