New Macbook sound problems

I have a brand new Macbook Pro 15inch. I also have a brand new Dell U2713H monitor. I hooked the video up via DP and from the monitor, I connected the external speakers to the monitor audio out port. I made sure audio out was set to the DP on the monitor and everything was working fine.. for several minutes. Then out of the blue, the sounds stopped working. I double checked and the settings were right. I flipped settings to internal, it worked, back to monitor and it didn't. Odd, it was working before. I unplugged from monitor and plugged into headphone jack and it worked, put it back on monitor and it stopped again.

Anyways, I'm not sure when/why it started working again, but after working for a couple minutes, it stopped working again. No idea. I posted the question on the dell site and they have no idea and recommended for me to post the question here. Here is my original Dell Forum post if that helps: http://en.community.dell.com/support-forums/peripherals/f/3529/t/19646967/