What I would do is get a replacement set (couple matched sets) pronto… like from The Tube Store. If this solves the problem, then go get some from Audio Research (They do extensive testing and I like supporting them)… or Upscale, if you want play with fancy ones… then the first set you purchased become your backup.
This is me… based on my priorities.
I always like having an extra set around. Just in case… they don’t act strange or fail often. But it is great to have a set in case a tube develops a whistle of some other idiosyncrasy.