Inspired from Psyop Softimage ICE Workshop by Jonah Friedman.
ndickson
Maybe it's my paranoia from doing it wrong so many times, but is there correlation between those random values on subsequent bounces? It kind of looks like there might be, but it's hard to tell for sure without checking it over myself. If there is, you have to make sure that each ray's BSDF sampling seeds are unique (or alternatively, independent) from all other seeds, else you can end up with nasty biases, Moiré patterns, or poor convergence.
I wasn't using very unique seeds for each subsequent ray where the seeds were also using the same values.