DAM Broken tube?

When putting the KT90 output tubes in my new Rogue Cronus Magnum, I heard something rattling around in one of them. The other three are quiet. Does that mean the tube is definitely bad and I should not power the amp up?

I wanted to have it up and running in a couple hours.

When I picked it up at UPS, they had the box standing on it's side despite arrows on the box showing it should be laid flat and fragile symbols. When I pointed it out they said "Oh we don't do that", referring to following handling instructions on boxes.

sometimes pieces of glass break in the the tubes. It does not mean that the tube is definitely bad. Do you see any physical damage to the tube structure? If you have access to a tube tester I would check it for shorts.
I had that same thing happen a couple of times. The tubes worked just fine each time. It could just a loose piece of wire or structure that will rebond once it gets hot enough.
Have it tested for shorts, before installing and powering up. Generally; there will be no problem. I would hate to use my power amp as a tester though. A shorted tube could get ugly, in your output stage.
Agree with Rodman. I just lost a bias resister because a tube went bad. Fortunately, the factory arranged for same day service at my home, all under warranty. When trying out the socket with a back up tube, one of the back up tubes also had a rattling sound. Both tubes went back to the vendor for replacement. Trust me, you don't want to use the amp as a tube tester.

Further, no one can diagnose a tube problem without seeing the suspect tube, and even if the tube is directly examined, I still wonder. Good luck.
The rattle is one source of microphonics...likely a loose part, not necessarily a bad tube. A tube tester is a good thing, but does not tell all. jallen
I have had many power tubes rattle and never had a problem.
If it's a loose rattling then it could be a small piece of debris inside the tube. I've seen this mostly in vintage tubes and it's usually harmless.

More commonly, a semi-rigid rattling is caused by the heater filament banging around inside of the cathode tube (more likely with bigger tubes). Some tubes are just worse than others, even of the same type & date. Generally not a big problem, as the filament should have adequate insulating coating and the filament wire itself is unlikely to break. However, with the less than stellar quality control of the russian and chinese tubes - there will always be some "bad apples" out there.

I've actually noticed the worst examples of this kind of rattling on some vintage Mullard EL34 and some nice old 5R4GY rectifiers - and never had any operational issues with those tubes.

Obviously, it's not advisable to shake & rattle such tubes like maracas for fun - you don't want to them any reasons to fail. However, most of these tubes (even new production) can survive untold horrors in shipping and keep on ticking...tubes are is many ways quite robust.

The short answer is that your tube in question is PROBABLY ok, as long as it tested fine before shipping. I stick with tubes for their sound, but on the flip side you're going to have to start dealing more in "probably"'s rather than pure "certainties". I've had 1 tube catastrophe so far...last year an EH KT90 shorted out on me, with sparks and smoke (toasted a resistor); there were no warning signs beforehand. Reliance on Russian power tubes is a reality for me, and from now on I'll be buying from sellers that burn them in for me.
Thanks for the responses. It does seem to my uneducated ear that it could be a heater filament, I could not see anything rattling around.

Everything is working and it sounds incredible! Beautiful, deep sound stage.

I may have an interference/ground loop problem. When no music is playing, I'm hearing a mild to moderate hum or buzzing. The amp is in a shelf just under my TV and behind it is a power strip that the TV, BR,AVR and Rogue are all plugged into. There is also an amp right behind the Cronus that the cable company installed to boost my signal(would it be the main suspect?).

A couple feet to the left is a separate outlet that my turntable is plugged into. A couple feet to the right is an outlet the cordless phone is plugged into along with one of those small 2" desktop fans I was using to pull heat away from the amp.When i turned the fan off I heard a click through the speakers but the buzz remained.

Does this sound like a grounding issue or could it be a bad tube? Like I said, music sounds great just noticing the buzz when it's quiet.

I have a pro coming over this week to check my setup and get it dialed in. Could the buzz hurt anything in the meantime?
Found the source of the buzzing, it's my Plasma TV. LG 60PS60.

Any way to fix it? Is it hurting anything?