WGS dude had a blog article on populating 2x12 combinations. I cannot find the blog post, but tracked this down onthe website:
”The 12” Retro 30™ speaker is a brighter and more articulate version of the WGS Veteran 30™ speaker. The Retro 30™ also boasts deeper and tighter bottom end. This speaker is extremely versatile and comes alive on the dirty channel. For those who love to mix speakers, you should pair this with the Reaper™ or the ET65™.
Retro 30
Reaper
ET65
Also this: “Possibly the best WGS speaker combination we can recommend is the ET65 paired with a Veteran 30™. Your cabinet will sound more full and colorful than you ever imagined. If you are putting together a 4x12 cab, we suggest either an "X" pattern or the ET65s on top of the Veteran 30's.”
Veteran 30
I like that color, the grain peeking through, and I applaud thrusting the stoptail unto the bout, thus balancing the aesthetic… but, as the saying goes:
” Without a wraptail, you MUST acquit!” - Johnny Carson
Hmmmm. My usual response to popping is a leaky capacitor, but that’s typically in the Audio path.
Could it be the rectifier?
As an afterthought, check the long shielded cable that comes off the loop return and goes to a place at the other end of the board. It’s a tight fit and the plug in at the end can loosen with jostling. If it’s loose the M channel will cut out.