Today I took my NB to the mechanics. Was originally only going to my local, but his answer didn't really fill me with confidence, so off to another for a second opinion, who proceeded to confuse me further and by the third I was ready to throttle someone.
For quite a while, my NB8A's engine has had a knocking sound at cold start up that goes away in a couple of seconds as oil pressure comes up. It's similar to the way the NA HLA rattle works but this is a deeper, heavier sound and these are solid lifters. It's been present now through two oil and filter changes. Plugs and leads have also been changed during that time. I've worked out it's from the rear of the engine, quite loud with screwdriver to my ear and on rocker cover, but it's been difficult so far for me to tell if more pronounced from top or bottom of engine. The engine's always very quiet at idle and through the lower revs, but knocks again under acceleration at 3000 rpm ... fine under deceleration ...
All three mechanics had a good listen and short drive to hear under load ...
Mech 1 says it's oil leak back, probably due to a faulty oil filter as they've had a few faulty ones recently ...
Mech 2 says it's probably piston slap, could be end bearings, but probably not, as it would probably have packed in by now, so just put up with the noise until it gets a lot worse then bring it back ... an awful lot of "probable's"
... anyway, not being very mechanically minded, I had never heard of piston slap and had to Google that one 
Mech 3 says it's a worn cam ...
Now, some credit where it's due - not one of them charged me anything even though I asked each what I owed them for their time ...
However ... only conclusion after a day of driving from mechanic to mechanic ... I need a drink ...
Feels better
... off to open a bottle of red ....
