Why does my mac have sound then when I put it on again its gone?

[iMore Question]

I upgraded to yosemite and when I plug in a usb it takes the sound away. If I close down it comes back but it alternates between on and off

 

[Bigeric23]

You just now upgraded to Yosemite? I haven't had any issues with USB and sound, and I've been on Yosemite since the beta.

What type of Mac do you have?