engine knock and t-stat problem

[cmhass2]

Just pulled the plenum to repair a vacuum leak. It was repaired successfully and this brought down a high idle. Drove fine for a couple days. I noticed engine knock last night for the first time in the four years I have owned the car. I have also recently replaced the fuel pump assembly and fuel filter. In addition, I have noticed there is not much difference between the upper and lower radiator hose temperatures (thinking t-stat may need replacing-directions on how to do so would be much appreciated). Any ideas as to what may have caused this or how to fix it. Was it a transient one time thing? Was it related to my other issues? Thanks for any input in advance!!