@Mark Here's more details about how to reproduce:
Departure
Load flight
Select "Turnaround" state from EFB
Sound appears
Set EXT AC to OFF or Close FWD PAX DOOR from EFB
Sound disappears
Set EXT AC to ON or Open FWD PAX DOOR from EFB
No sound appears!
Arrival
Land aircraft
Decelerate below 15 kt
Sound appears
Connect Ground Power & APU
Set EXT AC or APU to OFF
Sound disappears
Set EXT AC or APU to ON
No sound appears!
This indicates a bug, since I cannot imagine any situation where such sound could appear in line with the actions described. While the sound may be similar to ground roll rumbling, it can also be a clacing induced by air vent/flow or similar - in the end it's up to you to define the sound origin, since there is no other source like FS Realistic etc.