Engine Knocking?

[usfstud27]

I have a 1994 GS300 that I recently made a few repairs (New water pump, thermostat, timing belt, serpentine belt) to. After drivng it for about 20 miles, it has started making a knocking sound that sounds like a valve or lifter towards the back of the engine. Also, about a min after I shut the car off after driving for some time, It starts to make a boiling sound in the water system. Unfortunately, my temperature gauge on the dash does not work. It drives good and coolant does circulate trhrough the system while driving. Any ideas on what the problem could be? I did just put some sea foam in the crank case and water wetter in the radiator to see if it might help....prob not but I'm crossing my fingers. Will some of you DIY veterens please offer some ideas and solutions. Thanks-