I believe it is the same as Yosemite found here: Link to this post
For OS X Yosemite 10.10 set the following in Safari Preferences:
1. In the Advanced tab, set "Stop plug-ins to save power".
2. In the Security tab, set "Allow Plug-ins" by Internet Plug-ins and then click "Website Settings..." for it.
3. Find the media type you want to stop auto-play in the left hand column(s).
Most non-Flash videos (mp4/h264/HTML5 video) will be "QuickTime".
4. Set "When visiting other websites" to Ask to click to start, or Block for permanent disabling.
5. Click "Done".
Safari will play the video(s) on a page for a brief period before stopping to save power, and the noise will cease.
Clicking on the play button on the video will start the video and audio again for viewing when desired.