Help: Tube Power Amp - Popping and Cracking

I'm experiencing loud popping and cracking sounds on my left channel of my Jadis DA7. I swapped all 18 tubes between channels one pair at a time with the preamp off but it still stayed at the same channel. I even swapped the speaker terminals. I'm still new to tube amps. Anyone experienced this before? Thanks.
THe procedure you used should have revealed that there is a bad tube somewhere. Since the problem still persists and did not shift to the right channel when you moved the tubes, it's up for grabs. I would consider having it looked at by a professional.
Thanks cyclm, hope it's just a faulty socket. There goes the quick fix and in comes 'silent nights'. I suppose one can only enjoy an ageing tube power amp with another one on standby. Cheers!