Go to SteamVR -> Settings -> Developer -> Display GPU Preformance Graph in Headset. Make sure it's disabled by unchecking the box. This is not showing the volume but it show the speed at which your GPU is rendering the scene. If the number is above 11.1ms, your under 90FPS and are dropping frames.
To reach Viveport's customer service team, email email@example.com
To connect with a live support agent for hardware support, go to www.vive.com/support, click on "contact us" in the top righthand corner, and then opt to speak with a Live Chat agent David R
Technical Specialist - San Francisco, CA; Monday-Friday