Supermicro C7Q67 or PSU alarm sounds when boot attempted with AMD Firepro S9000 GPU

Question

I have a Supermicro C7Q67 motherboard that I had working as a Windows Server 2016 RDS machine. It was a simple set up and I was only planning on using 1-2 VM clients with RDS, but I had been using it with a GeForce 740 SC GPU and thought I should get a 'real' server GPU, since the drivers for GeForce are temperamental on Server 2016.

So I just received an AMD Firepro S9000 GPU today and plugged it into the x16 slot, and as soon as I turn on my computer I am blasted with an uninterrupted alarm sound (not beeps but a steady, constant, AWFUL sound).

Needless to say, I turned off the computer each time I was greeted with this horrifying result. I looked in the C7Q67's manual, searched all mentions of 'alarm', and the only thing I really found referred to memory - to remove it and try turning on the motherboard again.

Well, I tried that and when there's no memory or GPU in it, it emits a comparatively pleasant-sounding 'beep beep beep'. Put the memory back in and it goes away. Put the GPU back in (memory or no) and 'WHAAAAAA'!!

It sounds as if it may be coming from another component, because the MB speaker doesn't make a noise like that (referring to the sound made by the motherboard when no memory present). My thought is maybe it's the PSU, but I have never heard of a PSU having an alarm.

I am also thinking it might be the PSU because the S9000 is a fairly herkin' GPU (225W TDP) and I'm currently using an Antec Earthwatts 380w PSU. CPU is an i7-2600 (either 69w or 75w). No spinning disks or other components except for a Samsung 860 EVO. Seems like it's right at the line as far as load to me.

Can anyone shed light on this subject? Ever had this happen before?

Edit: When I was adding my fancy 1000w PSU I had just purchased, I realized I had forgotten to plug the PCI-E connector from the PSU into the video card. I am thinking that was the issue all along, and not the previous PSU.