Drive Shaft Click sound maybe...? Help.

[Cisc0]

I swear shit only happens to my vehicle when my wife drives it. She claims there is a clicking sound upon start up coming from the middle rear of the vehicle and that when she put the vehicle in reverse and throttled it she hears a click, click, click then again when she puts the vehicle in drive she hears it again but it goes away after reaching a 10-20mph speed. This morning I rolled down all windows to try and hear what she was talking about and she was right. I am thinking flex joints in drive shaft are failing but no sure. Can someone please chime in to what can be a possible culprit?

Thanks in advance for replies.