I take it's the same jack to the speakers.
Try another speaker set.
Just put together my new computer, and quickly found out that only the left speaker puts out (somewhat noisy) sound. What's curious is that when the speakers are connected to another device they work fine. Also, when using a headset the sound from the computer works fine also. I am using the jack connection on the motherbord.
What I've tried:
Installing new realtek drivers
Checking connections and rebooting
Motherbord: ASRock X99 Extreme3 LGA2011-3 ATX
RAM: KINGSTON HyperX Predator DDR4 2666MHz
Processor: INTEL Core i7-5930K 6-kjerner 3,5GHz LGA2011-3
Speakers: Logitech Z623 2.1