We have owned the Bongo for about 14 months now. Purchased from Ian Taylor.
When we got it there was a bit of a knocking at the back so on the first service (6 months) Ian replaced the two rear drop links and that cured it, then about 3 months later I started to get a bit of knocking from the front nearside so presumed it would be the front drop link(s). I waited 3 months until the next service & MOT and mentioned it. It turned out it needed a new drop link for the MOT on the Offside. So that was replaced but the nearside was said to be fine.
The knocking has continued though

So I bought another drop link from Ian and fitted it myself today, however I became doubtful of the need for a new one as soon as I started to remove the old one! I was able to unbolt it with ease - no need for cutting. Handling it once removed confirmed that it feels absolutely fine.
I fitted the new one anyway so that it has had all new drop links in recent months.
However as I feared once I took it out for a drive the knocking was still there

So does anyone have any ideas on what it could be?
I can't go and make it happen, but I only had to drive two streets away to get it to happen on my test drive.
It isn't a constant knocking noise, just two or 3 knocks every so often.
It tends to happen when turning and using the suspension at the same time if that makes sense.
Rough road can sometimes make it happen.
It happens most when cold, once you are well into a journey it doesn't seem to knock at all.
It happens at any speed but doesn't sound speed related.
I can go and drive round in full circles forwards and backwards without it knocking at all.