Might be the pads of your toes bunching up against your footpad.
Try using toe socks as liners and see if it helps.
I'm a big fan of the Zensah for high knee compression and Injinji for toe socks. For a Spartan, just because of the rope climb and I do S-Wrap, I'd probably use at minimum something like these. The Zensah can get expensive though at ~$45 for an socks and ~$35 for a sleeve.
Mudgears are very thick from what I'm told, which I'm not a huge fan of because they get hot. I live in Florida, so staying cool is mandatory.
I started using Injinjin toe socks as liners a few years back and I've had very little trouble with my toes since. They're not that cheap, but theyre still in good nick even though theyre thin and theyve done a fair bit of mileage.
these help, I wear these under my normal synthetic socks