Grounding issue or failing cartridge?

About 6 months ago I switched from a Grado Ref Platinum cartridge to a Shure V15VxMR. Everything was great for many months. Several weeks ago, the soundstage shifted dramatically to the left. Upon closer inspection at the speaker, the right channel was not only quieter, but sounded “far away,” slightly distorted, and was accompanied by hum.

At first I thought the phono stage of my preamp was the culprit. I plugged my phono cables into a different input on the preamp but the same problem existed. Now thinking the phono cart had somehow gone bad, I switched to an old Ortofon cart and the problem disappeared.

Refusing to believe the new cart was the issue, I remounted the Shure cart and the problem was still gone. I figured one of the connections to the Shure had been loose and was the source of the original problem.

This weekend, the same problem returned and the old “unplug it and plug it back in” trick is not working. I’ve checked all of the connections and have found nothing. No other system changes have occurred during this time and all other inputs function normally.

If anyone has any thoughts or suggestions for further troubleshooting, I’d greatly appreciate it!

Associated equipment:
Rega Planar 3 – I am the second owner. It looks as though the first owner swapped RCA cables. It is a simple 2 RCA arrangement - there is no ground cable. Has worked fine for 5+ years.
NAD304 as preamp
Sonographe SA250 power amp
I would double check the interconnects that plug directly into the cartridge for a possible short. They tend to be pretty fragile. I wouldn't imagine your cartridge would only last 6 months. They usually take about 1-2 months just to break in.

Check for an intermittent short in the phono cable,or in the cartridge leads connected too the phono cartridge.
Double check your alignment. If the cartridge has shifted it will definitely affect the staging.A tiny amount of movement is enough to really mess with the sound.
Thanks for the help - it was a short. I carefully removed the plug on the cartridge end of the tonearm without pulling on the leads themselves only to find the red lead was nearly broken in two. Time for a rewire, I suppose.

I prefer sending the tonearm to someone else for a job this tedious. Does anyone have any experiences to share with this process? Prices seem to range from $150-300 (Brit Audio, Expressimo, etc.)
Brit Audio did a Fantastic rewire of my RB300. A real nice guy and 2 day turnaround.
The Incognito upgrade was easily the most dramatic improvement I've made in my system- and I've made many changes over the years.
I recomend the structural mod while the arm is out too.