gyozadude

I have had issues with similar brake shoe compounds from Tektro on both V-brake and cantis and it's primarily with the front fork and some combination of rim wall finishes. Not every rim type will set off the squeal. And for me, it was primarily the front only. It always looked like the wheel rotational direction will cause inward push on the brake posts on the rear with primary touch point near where the seat stays are, providing better rigidity against vibrations. On the front fork, however, the primary contact is fore of the posts and the stress is more cantilevered. So you'll get unconstrained vibrations if you can hit a harmonic, and oh that sound was great joy, NOT!

I had to toe-in the stock black pads considerably to avoid any grabbing on a welded/pinned seam joint that will set off the micro-vibrations. And even if I did extreme toe-in now, I was likely to get some vibration once the pads wore and if the rim surface wasn't ever worn into a grooved state that probably changed the nature of the pad to rim surface contact. At least that's what I thought did plague me for a while.

My solution was experimenting with various brake pads. The Koolstop half-n-half pink/salmon and black compound shoes ended up being the most quiet, so they're up front and it wasn't a perfect solution. I then had to ride through a mud-pit, squeezing the front brake until the grit wore many small grooves into the front did the final trick to keep it all permanently quiet.

Hope that helps. YMMV.