I suspect something loose or worn which hasn't been picked up by the mechanics.

Check caliper securing bolts, remove pads and inspect properly check anti rattle springs and sliders and caliper pistons arn't seized, clean and lubricate as necessary on refit, check condition of inside face of discs, remove rear drums and check shoes and wheel cylinders for security and correct free movement, check all suspension and steering bushes including anti roll bar and shocker mountings and bushes.

One other thought is that a CV coupling could be running dry but i would have expected that to be noisy on turns, still worth checking.

The symptoms sound very similar to a common fault whch used to afflict Rover 800s. The sensor mounting blocks were made of mazak and when they corroded they squeezed the sensors to death. The fault would be intermittent at first and this is when the symptoms similar to what you describe would appear - ie the ABS would chatter below 5mph.

I'm sure more modern cars don't have the same design failing (designed by Honda, of course), but it might be worth checking all the sensors and associated wiring for damage and continuity.. Unplug and reconnect at all points in case it's a connection issue.

As above, also check for mechanical issues, ie anything loose, including wheel nuts.

Have you tried invoking the ABS? And does this bring on the light?