What was there to not understand? There are lots and lots of different noises that can be described as a "knock" - just saying "knocking" isn't descriptive enough to have complete strangers with no access to the car give well reasoned advice.
That said, if it is more like a thunking and it is present without having the van moving at all then the engine probably needs more than rod bearings - which was an odd thing to leave out of your initial post. Presumably the rod bearings were supposed to fix the knock? If you hang around and stick your head in various places can you tell where the knock is coming from? Up top? Down low? Left/right side?
One thing you could do is go comb Youtube for videos of engine noises - find one that acts just like your mom's van and post a link.