Wiggle kt170 base

Any play in the tube’s base / glass , you should get rid of that tube immediately.   If the tube is loose in the socket the socket’s holes need to be re-tensioned.  They are not gripping the pin well.   This can potentially be harmful and should also be addressed 

If the tube is loose in the socket, one way to address the problem is to re-tension the socked holes as mentioned above.

There is an easier way to address the problem I have used several times and was recommended by a distributer: using a very small pair of pliers, gently alternate bending every other tube pin in and the next pin out.  Less than a hair is all it takes.

If the glass envelope is not glued to the base well the tube could be compromised and could prematurely loose vacuum.  If the silver getter turns white that’s what’s going on 

Changing tubes should not cause clicks, pops or hissing. If the socket is loose, get it replaced or repaired ASAP. And if the tube is what is loose @jetter give perfect advice.

Unless you swap the tubes in both sockets to see if the hiss stays with the tube or the socket, there is no way of telling if it is a bad tube or a bad mechanical connection. You could have a bad tube and it decided to show itself that day. Or you could have pulled the tube out or inserted into the socket in such a way that loosened the socket connection. Or... the socket could be soldered to a circuit board and the high heat compromised the solder joint and wiggling tubes in and out of that socket broke the solder joint.