You're not the only one recently, check out some of the threads here and in the Disco forum!
Anyhow, check some of the following:
rear A frame balljoint
Rear trailing arm bushes incl torque
front radius arm bushes incl torque
all 4 UJs for play and bolts being tight
Wheel bearings and steering swivel bearings
foreign objects jammed inside wheels/wheels damaged
wheelnuts!!!!!
If the above fails we need more detail, is it a repetitive clunking, is it speed related, under power, only in reverse? Where does it sem to come from? What have you been doing out in the snow (you jammy g**, it hasn't snowed here since Thursday).
What year is your car, etc etc.