Anyone know what could cause a new small signal tube to "sputter"?

As I was setting aside time to apply Total Contact contact enhancer to my system a couple weeks ago I decided to put new 12AU7s in my line stage and 5687s in my SACD player.  The left channel had a somewhat intermittent "sputtering" sound.  Today, I took the line stage out of the system and switched the tubes and as fate would have it the "sputtering" moved to the right side.  Bad tube!  Once I took that tube out, and replaced it with a worn, but still quiet, 12AU7 all is well.  Just wondering what might account for the "sputtering" tube.
Likely a short that is causing the tube to intermittently arc. You might try taking it out if its socket out when cold, and while holding it upright, tapping it sharply on the side a few times with a chopstick. Sometimes the short is caused by small debris from the manufacturing process that gets caught in the filaments or plates during the tumbling of shipping, and, sometimes, one can jostle it out to the bottom of the tube where it will remain out of trouble. About 50% of the time I've been able to resuscitate a faulty, sputerring tube wth this method.  Power tubes too. Let us know.