Tube amp problem question

Hi Audiogon-philes,
I have a EL84 based new Luxman SQ-N100 tube integrated (10W). I have had it about 3 weeks. In the first week, purple sheets of 'flame' inside one tube with a hideous naked static like noise in one speaker forced a return to the store where it was checked, the tube replaced and I was told it was ok now. And it was for 48 hours and while I dont have the tube making strange colours I get the noise the moment the mute function cuts out after turning it on. Any thoughts? My plan, of course, is to take it back to the store.
Speakers are Rogers LS2a/2 and these speakers function perfectly with the previous amp, a Fatman iTube (12W). Source is usually an iPod dock.
I would say some other problem is causing the tube to fail...
I agree with Elizabeth. If you can swap it with a like tube from the other channel it would confirm it.
You should ask them to retube and bias if it is not auto biasing
The voltages on the the plates and the bias need to be checked. Could be a bad resistor.