I also experience this behavior with my 390x.
I've seen this reply given in this forum for this question on multiple occassions, and it sounds just like a canned response. And the part about not increasing power draw as it is only affecting the mem clock is not true. GPU Voltage absolutely increases due to this as well.
This behavior does NOT occur @ 120Hz, and I sincerely doubt that the additional 24 Hz would require to run the card full throttle. From 150Mhz to 1500Mhz memory and from 891mv to 1.109V?? (See screenshots below)
If an additional power/clock state is needed for the higher refresh, I understand that, but this drastic of a jump should not be required in normal desktop use (not gaming).
ALSO, there are users that have shown screenshots of 144Hz with no additional upticks in memory speed or voltage.
When is this issue actually going to be addressed, or at least acknowledged as a real issue.