Sounds like your CV axles. Have someone hold the brake and slowly move the gear selector from D to R a couple times while you watch the axles. If they are bad they will move around a bit.
I have blown about 3 sets of these guys and every time it was a new noise. One set was just a click at slow speed, another was a grinding sound at around 90, and the other was only under high speed cornering. Each decided a road trip was a good time to start making noise. After clicking 2 of the sets lasted 3K until I got home and pulled them, could have gone longer but they were VERY UGLY when they did come out. All the balls had fallen out, just metal to metal clanking around back there!

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1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4