It could be just a resonating sound coming from the drive line tubing. I may do a harder than normal shift every now and then. If you aren't feeling any odd vibrations, you are most likely good to go. Drive line vibs usually start to be real noticeable around 50 mph.
Happy Glamping, Norman & Elna. 2008 Winnebago Adventurer 38J, W24, dozens of small thirsty ponies. Retired after 40 years wrenching on trucks! 2010 Ford Ranger toad with bicycles or KLR 650 in the back. Easy to spot an RVer, they always walk around with a screwdriver or wrench in one hand!