The noise could be wheel bearing. Depending on if it is the inner / outer / center / periphery race that has gone the sound comes on different way , especialy when not going straigt forward. Very hard to find out which side it is until the sound is loud enough.
Once i splitted the differential on an quattro coupé . Was sure the noise came there from . Couldn´t find anny wrong. Then changed the right wheel bearing and at last the left bearing and there the noise disapered.

Bengt