Odd problem with TT setup...

Most likely its a resonance/vibration problem of some kind. Electrical faults- bad solder joint, frayed or damaged wire - usually results in cut-outs not pops. My first thought was slight bearing wear. Kick drum energy bounces the bearing and when it lands it generates the pop. But that would be more like a knock I would think. 

I can tell you how to test and prove its not internal wire, but you won't like it, way too complicated. To check the bearing/compliance/resonance idea place some small mass at the pivot point, adjust VTF, and play. To check compliance add a mass of a few grams like a penny or dime, stick on top of the cartridge with Blue-tack or tape. Anything temporary just to check the theory. Its unlikely, but so is everything else at this point, sad to say.

@MC... I did try the mass thing last night as suggested above, just to see. I added 2 grams of blue tac, no luck. I’m going to mess with it a bit more this weekend... maybe I get lucky. Otherwise, I’m going to just throw in towel and enjoy what I’ve got and maybe see about sending the tone arm into SME. Its about 12 yrs old give or take. Could prob use a service anyway...

Dear @geof3 : 12 years on that SME tonearm?, I assume you are the original owner. I don't know if the internal wiring in that tonearm is the same of more contemporary samples and if not then could be a good time for SME rewires it and at the same time can gives a check up to its overall specs, especially the bearings.

Now the V is a tonearm balanced design and the best way to use it is not in balanced way but in static way. Do you already did it ? if not rigth now is time to do it along its silicon damping ( tray. ).

Btw, I know that first than all you need to fix this pop trouble but after that and due to the quality top Atlas performance levels as the Hegel electronics and very good TT/tonearm you should change that good but average/medicre one phono stage that can't honor the true Atlas quality performance that can shows you with a way better phono stage that you can buy from Simaudio due that this Canadian company has very good and high level engeneering.
Your today unit works mainly through op-amps and its overload levels is really low at 2.2db. with a non accurated RIAA eq. for high differences in between both channels.
I know that you like what you are listening ( other than that pop. ) but in reality what you are listening is a " poor " quality against what the Atlas can shows you or to any other audiophile with the rigth phono stage.

With all respect you own a " Ferrari " that is running it with bike tires.

R.

A development... today, the right channel cut, very briefly... twice. Pretty sure now I have a tone arm problem. The question is, send it to SME and have it rebuilt/serviced or start thinking about a new tonearm?

The question is, send it to SME and have it rebuilt/serviced or start thinking about a new tonearm?

Both! Get a new tonearm and THEN send your SME in for service. Win win. Fun fun.