The activation of ABS at 0-6.2mph is always caused by sensor issues. Most commonly a specific sensor, sometimes a secondary condition busts the threshold for activation; such as fouled sensors or bad wheel bearings.
The only part that the squeeling contributes is the secondary activity (braking the threshold for activation). It is a very weak secondary activity and I would consider it a totally separate issue.
The ABS functions at all speeds but doesn't fault sensor activity below 10kph (6.2mph). The first place sensor problems occur is with the low speed activation usually in reverse while turning and passing over a vertical drop (like leaving my alignment lift - almost every car activates).
These low speed activations are usually just an anoyance. As they occur more often they will eventually wind up being observed at over 10kph which then sets the light and the problem then gets fixed (sometimes).
Bosch Master, ASE Master, L1
33 years MB technician