If an AudioSource is a child of a Rigidbody and Time.timeScale is set to zero, the AudioSource's volume will become stuck at whatever level it was at when the time scale was changed to zero

Steps to reproduce:
1. Open attached project
2. Open "RigidbodyTimescaleAudioTest" scene
3. Hit play in the editor
4. Select the game object "AudioSource_2" (which is a child of Rigidbody game object) and in the inspector assign some value to the volume
-You should hear sound volume increasing/decreasing depending on the value
5. Click on the "Game" window to set the focus there and press the space bar to set the time scale to 0
6. Assign different volume value to "AudioSource_2"
-Sound volume does not change

Actual result: AudioSource volume is stuck at whatever level it was at when the time scale was changed to 0
Expected result: AudioSource should be able to change volume when the time scale is set to 0 regardless if its a child of a rigidbody or not

Reproduced with: 2017.4.9f1, 2018.2.1f1, 2018.3.0a7