Recently, I notice the short burst of humming noise when I drive in
slow speed.  The noise seems to come about right before gear change
(automatic). It's most obvious when I drove at 44-45 mph. The noise
went away when I either easy off the gas paddle or speed up. The noise
went from barely noticeable couple month ago to very noticeable now.
Any suggestion/diagnostic before I leave my arms and legs at the
dealer.  The truck has almost 50k and no prior transmission/major
problem.

Thanks in advance.

JJ