1996 Suburban groaning noise

Sorry for all the posts. I'm probably driving you all nuts. I have recently discovered that my '96 sub will make a groaning noise from the driveline, on take-off after coming to a complete stop immediately after driving at sustained speeds over 70 MPH for more than about 4 minutes. Yes, this happens everytime the previous stated events is true, and no its not my imagination, its a loud groaning noise, it last about 3-4 seconds. My wife who was sitting in the middle row seat at the time noticed the floor vibrate under her feet when it made this noise. It will stop making the noise after a few more take-offs. Then I can't get it to make the noise again, unless I get it up to 70 MPH and do it all over again. I am going to take it to my drive-line shop, who also rebuilt my tranny a little over a month ago. I really am stumped on this one. Is something getting hot from the high speeds? I don't even know where to start, if you have ANY suggestions please do share as this is driving me crazy. Thanks!