I rode some gravel with the kids yesterday and noticed a rubbing sound at higher speed from the rear. I diagnosed it as the derailleur cable rubbing on the tire knobs. I have a 26x2.1 tire mounted in the frame, with plenty of space for wider, frame-wise. The bicycle sold with 2.0 tires, but has been through a wringer. I'm wondering if a different BB cable guide is the answer.

Cable is around 1 cm from chainstay centerline.

Current bottom bracket guide. Single bolt hole.