I need advice on a 300b tube

Here is my issue...I bought a pair of almost new  Linlai 300b B-Z treasure tubes  from a person who said that one of  the 300b 's had developed a humming noise after 5 hours of good (no issues) use in her amp. She claims that she heard a humming noise coming from her amp and so she put in her old stock 300b's and this noise stopped and then reappeared upon  reinstalling  her new Linlai 300b tubes. The noise she claimed followed into one of the 300b tubes..(I have no idea what that means by the way. How can a noise originate from her amp and then somehow get into her new tube? I do not think so at all and she merely got a tube that suddenly went bad.) She asked her friends can anything be done as her return window was already expired on these tubes. They said just leave  the problem 300b in her amp and let it  'burn in'  for 48 to 72 hours and see if it restores itself.  She got scared though and sold both of the 300b's cheap (ebay) and here I enter in. I thought she selling the exact treasure tubes I wanted and at half price?  ($99 plus tax) With her people's advice that might  actually mean only a small and temporary setback on one these tubes? So I grabbed for it. What do you think? Probably a really dumb move on my part right? (This is not the first time I have done this by the way).... Yet I am new to tube amps (not solid state though) and recently purchased a Willsenton 800i 300b /805 from china hi fi...a 100 lb. beast ....(and just to let you know this thing really  puts out some serious  music.... fidelity, sound stage,  its  all there and most of all is the ease of listening ....absolutely no fatigue whatsoever. But to the tubes---

I initially thought to  myself I'd take a chance so I bought these tubes. Yet now perhaps I should not have done so. I am thinking could this faulty 300b tube somehow pose a risk to my new Willsenton 800i  tube amp and  if not I might wind up with only one good Linlai 300b from the purchase. I then thought should I buy another Linlai 300b B-Z treasure to make for a  restored pair how would I know if it was a match to the original ? What do you think?  I know an impulse buy is many times a stupid choice but maybe one of you might have experienced a noisy tube that can repair itself as was suggested by these sellers' audio friends.....  I called a person where I live and he has many years experience in audio and he has never heard of a noisy tube repairing itself in this manner....What do you think? Is there a way to fix a noisy tube?   (Also this is off topic--but I have been a member of audiogon for years now and all my correspondence as in all entries in the forums and any of my buys---- all of it is gone. This happened a number of years ago as well. Has this happened to any of you?) I just looked on my site and I have only one entry from a year ago.) I have not given my password to anyone ...this is a mystery to me.