Tight Headset Still Knocking

My bmx bike's headset is as tight as I can reasonably torque it (and the stack has good clearance from steerer), but there's still some barely perceptible knocking if I turn the wheel sideways and rock back and forth while holding the headset cup.

When I last tensioned the headset the knocking disappeared, but when I checked again after some riding it had returned...

Does this just mean it's time to replace the cartridge bearings? Or have I done the dreaded head tube ovalization?

Thanks in advance.