Tubes sound like a broken lightbulb

I have noticed a few adds lately as I have been shopping for some tubes like yours that a seller or two has mentioned in the add that the tube had the same issue as you have with yours and that it was not an issue with its performance. I did pass on these, so don't know if there was an issue or not and appreciated knowing the fact before hand. 

Depends upon how hard you shook them to elicit the sound you hear.  Don't forget those octal triodes have a large glass envelope with substantial metal and mica structures inside.  I do believe that if you shake such tubes GENTLY, you might hear that sound.  And I also believe that if you shake them vigorously, there is a good chance you could cause the damage that would lead to that sound of a broken light bulb.  So, if you can honestly say you didn't shake them vigorously, why not give the tubes a chance to see if they work OK?  You might be fine.

I agree with @lewm , give them a try. It could be part of the structure you hear, but it would not be a very loud sound.
If there is a rattling sound, it could be a small piece of the plastic base is loose inside. I’ve had a couple of these.

In any event, contact the seller and ask what he thinks it is.

Some heaters employ a spiral filament, which shakes exactly like an incandescent lamp.  Should be fine.  What really matters are the microphonics generated when in circuit.  Tap the glass with a pencil lightly.