1998 AWD XC rumble/growl

[PAKCF]

Have a 1998 V70 AWD XC. Above 30 mph there is a rumble/growl that increases in pitch as I increase in speed ( likely happens below 30mph but I cannot hear it). This is not linked to engine speed or revs, but it is directly linked to road speed; it stays the same when I shift the car into neutral. Dealer checked bearings and said they were OK, and then said it was tires I am unhappy with that suggestion; they which look fine and undamaged and the noise remains whatever road surface I am on. Someone suggested engine mounts but they look OK (I cannot really tell except they are still there)
ANy thoughts? thanks