Popping sound when turning my Cayin TA 30 on/off

Hi. I am very new to tube amps. I have enjoyed my used Cayin TA 30 tube amp for a few months now, and all has been fine until the past few days. When turning the amp on or off, there is a loud uncontrollable (volume is OFF) popping sound that lasts a few seconds. (Happens while a tube is warming up or cooling down?) I assume this means a tube is gone. There are 4 EL34's , 2 12AX7's and 2 12AU7's.
Where does one get a tube tested? I have a voltmeter. I assume I need a tube tester to figure this out. Wanted to do some tube rolling anyway. Any suggestions for upgrades?
This sounds like a ground loop problem. Search this board (or others) to find exactly how to fix it, I think the general rule is that you only want to have one 3-pronged plug going into the wall. I had a very similar problem and this turned out to be the cause.

Tube testers can be bought on eBay, they run about $40 and up depending on what you get. Mine came from my grandfather, who bought it at an auction for a buck or so and then gave it to me.

Hope that helps
Thanks for the response. It was actualy just a bad el34 power tube. Got a matched set of 4 new stock Mullard EL34s on sale from Tube Depot for $90 overnighted. Just in time. Picked up a new set of Meadowlark Blue Heron 2's today, and I don't want to be popping with those hooked up.
Thanks for the reply.