I had this problem when first installing the UMIK-1 on Windows 10.
It was pointed out to me through the chaps over on the REW forums that I probably have the volume of the mic too low.
Thought I'd already looked at it, but it seemed not.
If you don't know how to get there, right click windows bottom left, select system, then sound.
Once in sound, click sound control panel in top right.
Under recording, double click microphone and then levels.
I moved mine up to 100 and started from there, had to turn it down a bit in the end.
Hope this helps