Since it happens kind of after the bump and since the boots on your axles are broken is it possible that you got some rocks or other such items thrown into the boots? Then at low speed you go over a bump and it tosses on into the axle joint? The noise you hear is the rock or whatever being crushed and the sound of metal crushing it?

Kinda fishin here. The boots are not critical right now but they will be. With the grit etc that you pick up off the road from driving it will wear the axle joints inside the boots out pretty fast. That is if they are open and not just cracked.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique