moisture on the inside of the oil cop

What is your question?

just purchased with 52000 miles had the oil changed at 55000 miles shortly after, one of the lifters started knocking, I had the oil changed again, as I watched I noticed there was moisture on the inside of the oil cap The tech wiped it clean and checked the PCV and the vac line appeared not to be pulling the air out. Nothing more was done and I drove off within five miles the lifter stopped knocking. The valve tapping returned and I'm still getting moisture in the oil cap. What is going on here?