Trembling sound with Dell monitor/speaker bar

I’m streaming to a Dell 2408WFP monitor and speaker bar via HDMI. The sound is trembling when I play video or audio. However, if I turn off the monitor and turn it back on, it becomes normal. Unplugging the HDMI cable and plugging it back has the same effect.

Not sure how to trouble shoot it. Anyone have similar experiences? I could potentially leave the unit on all the time to avoid the problem, but then the problem is there is no blank screen saver.

Thanks.