On ice if you brake hard your wheels lock up and brakes rumble and groan why?

because youi probably have ABS breaking system which does NOT lock the brakes up on ice but grabs the rotors a 100 times a minute making that "groaning" noise you mentioned which is totally normal. Be glad for that groan. If you were really 'locking' up as you say-your car would be just an unstoppable sliding object with no way to control it except for some minor corrections by swerving r or l. That groaning is saving your life. And-If your ABSOLUTELY positive you don't have ABS then the rumbling and groaning are from what? Passengers praying? But locked up brakes on ice should not be rumbling and groaning. good luck