I think that these engines do get very noisy as they get older, but they still seem to be reliable, it could be piston slap due to the pistons having very short skirts, really not much you can do except get the engine opened up and if necessary replace the pistons and rings, and check the bores to make sure that they are now not too oval. If they are too oval, the engine block would need bored out to reduce/remove the wear and a suitable bigger set of pistons and rings fitted.
I've read on someone, with the earlier BBY or BBZ engine in a VW Polo, changing all the hydraulic tappets and ending up getting a bit annoyed as the noise was still there.