Hello All! This is my situation When my S90 with 127K miles is placed into gear a rumbling sound starts and goes away when out of gear at idle. I have flushed all fluids and filter change, inspected trans mount and installed new shift linkage rubber bushings. All seems functional and working. Trans shifts throught the gears fine. Could this be a low oil pressure issue or idle? Thanks in advance!

 

Without being an expert in transmissions, that sounds like it could be something related to the torque convertor.