Been trying to shut off that sound myslef. Best I could do was run a logcat while going in and out of service. After three months of continuously riding in an elevator I think I may have found something.
I'm not sure if this is it, and if it is, if anything can be done with it. Hopefully there is someone who understands this stuff.
I/TelephonyRegistry( 170): notifyServiceState: 1 home Searching for Service Unknown CSS not supported 75 4162RoamInd: -1DefRoamInd: -1EmergOnly: false
I/TelephonyRegistry( 170): notifyDataConnection: state=0 isDataConnectivityPossible=false reason=null interfaceName=null networkType=0
D/BT HS/HF( 440): BluetoothPhoneState : handleMessage : 1
D/PhoneApp( 440): mReceiver: ACTION_ANY_DATA_CONNECTION_STATE_CHANGED
D/PhoneApp( 440): - state: DISCONNECTED
D/PhoneApp( 440): - reason: null
D/PhoneApp( 440): SignalInfoTonePlayer.run(toneId = 86)...
D/NotificationMgr( 440): hideDataDisconnectedRoaming()...