It is a tube. If it is happening in all channels, it is a power tube. If it happens in only one channel, it'll be the preamp tube assigned to that channel.
There is honestly little reason to go about this thinking that there must be something wrong with EDs in general. You have a tube amp -- which means that tubes go bad. Luckily you have a Mesa. No bias necessary.
Just an FYI -- your title post is borderline slander. Remember, people only sound off when there is something wrong, at least more often than when things are going great. These forums are collections of suggestions and alleged issues. If people aren't discussing problems they are having with a piece of gear, then they are bragging about a new amp they picked up -- all the while glorifying it as the best thing EVER. Until, of course, they grow tired of it and seek something new. My advice to you, coming from someone who has made similar mistakes in the past -- don't get into the habit of making broad generalizations such as, "Yet another Electra Dyne with problems." Yours may have a problem, but it doesn't mean that there is a problem with the amp line as a whole.
I went through the same thinking too a long time ago, when I first started using tube amps. You aren't the first, so don't feel bad. Chances are good that you have a bad tube. Why? That is usually what the problem is. These are tube amps and these are the type of problems associated with them. Hence one of the reasons why Mesa repackages tubes -- they are trying to minimize the likelihood of getting bad tubes put in their amps.
