Don't think there is a noise blanker plug on the TR-4, is there?
Me thinks it more likely to be poor connection on a valve base so have been looking at how to clean them.
Remove each valve one at a time. Spray DeOxit into the valve socket. While the valve socket it still wet with DeOxit, "wiggle" the valve while reinserting it into the socket. Repeat for each of the 20 valves.