Onboard sound choppy when HDMI monitor is connected?

PerfectBlue97

I have a Gigabyte X740 Aorus Ultra motherboard and a GTX760 graphics card. I have the current stable build of Windows 10 (Not insider)

I'm currently using the fibre optic output on the motherboard and a Samsung 7.1 amp for all of my sounds.

I've been using DVI to connect to my monitors, more out of habit than anything else.

I tried connecting one of my monitors (Ilyama prolite) using HDMI.

I use the Windows sound mixer to set my Amp (Optic from motherboard) as my default device as the Prolite's speaker is rubbish.

Now, all of the sound to my amp is choppy. It will play for several seconds and then cut out for several seconds. It does this in all software from games to Groove.

It still does this even if the monitor is switched off.

The only way that I can get the sound back to normal seems to be to unplug the HDMI cable and reboot the PC.

Essentially, my motherboard sound drops out repeatedly whenever my graphics card is connected to a device with a speaker. Even if the speaker is not being used.