A lot of Radeon GPUs in the 5th, 6th and 7th generation (and some Nvidia GPUs as well) have a known multi-monitor issue of VRAM clock speed being maxed out at all times.
This leads to increased power consumption at all times which can stack up and affect your electricity bill.
Why am I making this post? Because I struggled with this for a while until I found a solution that works. It really depends on your setup, but I'll gather every solution I've tried here and tell you what worked for me.
For context, I have 2 monitors - 1440p/180hz + 1080p/144hz and a RX 6800 XT.
Solution 1: Using a custom display resolution
Following this solution, you'll have to create a custom resolution in the AMD Adrenaline Software:
Select your main monitor, pick CVT - Reduced Blanking and set your monitor's refresh rate appropriately. Sometimes you'll also have to lower the G.Pixel Clock (kHz) by 1 for the Save button to work.
If that doesn't work, you can also try doing it for your secondary monitor. Same settings as your main one - CVT - Reduced Blanking + correct refresh rate.
Note: This is the only solution that worked for me.
Solution 2: Messing with FreeSync settings
If you have a FreeSync compatible monitor, try turning FreeSync off or adjusting it from Basic to Extended or vice versa.
You can also try turning off FreeSync from the AMD software itself:
In my case, this didn't really help and the results were rather random.
Solution 3: Setting a lower refresh rate on your second monitor
If you have 2 monitors, one being 180hz and the other being 144hz, it might help if you downclock your 144hz monitor to 120hz.
This way, the number is dividable by 60 and synchronizing frames should be theoretically easier (can't tell for sure, this didn't really work for me).
Conclusion
That's about it. If you have a solution that's not listed here, you can join our Discord and mention it and we can add it to this post for future readers 🐢