[molehole]

Probably is the pump in the transmission. My Explorer doesn't do it but my 96 Blazer has done it for the last 20k miles or so. The cars runs great it just whines constantly. I had the fluid changed along with the filter and my mechanic says they will do it if they run low on fluid. Mine actually ran low on fluid and I didn't check until the damage was already done. My advice would be to check the fluid to make sure it isn't leaking out anywhere and make sure to check it in Park, on a level surface when the car is fully warmed up. Just because it may have been rebuilt doesn't mean that it is perfect. Many times Transmission shops do terrible work so the trans will fail right after warranty. You may want to go have a professional shop vacuum out all the old fluid because you only get out a 1/3 or so by dropping the pan. The sound will go away when it shifts into overdrive as you are describing. It is really not worth tearing down the transmission to fix it. Good Luck and keep us posted