I have not solved it yet. Saturday, I ran my tank almost empty and filled it with 3 gallons of soybean oil. It made the engine very much quieter so that I could listen more exactly what the sound was. I replaced the pressure valve assembly which greatly reduced the sound and gave it much more power now, but it did not get rid of it at all. Anyway, running on sybean, I could tell the sound has a much more mechanical nature like actual metal-metal heavy tapping. At this point the last thing I can do without taking off the head (Which won't happen as I don't have the time/cash/tools to do it), is take off the lower oil pan on my next oil change and have a look at all the bearings I can get to.

If that fails I will just have to live with it until it blows up
It's lasted 8 months now, so I'm sure it will be fine.