Sizzling Sound on Yosemite in Multi-Output (Aggregate Device) from the 2. Device I recently wanted to play my music through multiple output devices at once: 


My Macbook Pro's internal speakers
Bluetooth Speakers


As i have found from the internet i have created a Multi-Output Device through Utilities/Audio MIDI Setup, and it works. The problem is, the 2nd device (not the one which is selected as master device) gives a sizzling sound, which is independent of the source. So, when I select the Built-in Output as master, the bluetooth speaker sizzles, and when I select the bluetooth speaker, my built-in speaker.

Does anyone have this problem?
Try making sure that your source format (Hz) and bitrate are set to the same on both devices.  My guess is that if they are different, you may have one receiving information at one rate but transmitting as another.