I've tried being consistent; I don't think that's it. Those marks are there from the moment the image starts to show, whether it's within the first 5 seconds or after a minute or 2, and they remain there. Because of that, at first I thought it was how I was inserting the print into the developer, because I often use the "plop" technique rather than a gentle slide into the tray. I kept getting the ripples no matter what, although about every 5th paper or so turned out OK.
I think the answer is as some have already suggested; it's the paper. All ripples have all been on the Ilford warmtone, both the 8x10 and the 11x14. I have no idea why; it's not old and it's been refrigerated up until last week.
Today I spent an entire ripple-free session; I went with my old Agfa MCC. (I did test one sheet of the Ilford, though; ripple!) I will try the Ilford in normal developer next chance I get.