Sound problem with Dell S2340L

Hi I just started to experience issues with the sound coming out of my speakers, which are attached to my monitor, the only way I can think of describing the noise is that when people talk they sound like a Dalek, from Doctor Who :D Its like a two sounds with the second just behind the first and deeper.

My monitor doesnt have speakers, so I use the earphone connection to attach some basic speakers and connect the monitor to the Base Unit with HDMI, in the last couple of days all sounds coming from the speakers have distortion.

If I switch the speakers from the monitor to the Base the sound is fine, but its more convienent to have them connected to the monitor, Im not too tech savvy so Im a bit lost as to what to try to try and fix the issue.

I have checked drivers, which show as up to date, Im assuming its the monitor thats the issue as theres no problem with sound when connected to the base, can anyone offer any advice on what to try please?

Ive done a Hard Reset and a Factory Reset but the issue still persists and tried a different HDMI cable.

Im on windows 8.1, though I dont know the video card info, if I open Devices Manager it lists the following under Sound, Video and game controllers;

Bluetooth Audio Device

NVIDIA HIGH Definition Audio,

NVIDIA Virtual Audio Device (Wave Extensible) (WDM)

Realtek High Definition Audio

Not sure how to check these things

Is there any reason to maybe tinker with the graphics card? I notice there was an update round about the time the problem began, but Im not sure how to check this.

Thanks in advance :)