rear end noise

hi everyone ive got a 1997 safari. I got into a accident last week and the body was done but they said the rear lest axel was bent so they replace it with a used one know im noticing that the rear diff is makeing a noise sounds like bearing noise when let up on the ga and coasting. also notice a little leak fro the diff. they said they replaced the diff oil also. Does the diff oil need anti foam additive as well. Could this be the sound its making ? i dont think they added any anti foam.

Gear oil should have sulphur EP additives, moisture displacers, and foam suppressants already formulated in. There is no need for any further additive.

A used axle might have a failing bearing, and after sitting in a salvage yard for however long it did, there might be a slowly increasing noise from a marginal bearing as it deteriorates further from driving. If the replacement axle is noisy, the salvage yard should replace it free. They always do around here. Either the repair shop should warrant the work or take it out of the salvage yard's (part supplier's) hide.