You say there is a sound regardless of whether you are pedaling. I have suggestions but I am no bike mechanic so follow them if you want but you have to take responsibility for any failure.
(1) What about speed? Lower your seat. Do you hear it sitting on the bike (weighting it) and walking it? I would slowly walk it and maybe mark my tire with chalk at the lowest point when I hear the sound.
(2) Do it without the battery. Unlikely but easy. But does the sound go away?
(3) Do it only if it is safe. Completely loosen the rear brake cable. Does the sound go away?
(4) Remove the rear fender. Does the sound go away?
(5) Unlikely. Remove the chain. Does the sound go away?
After that, it has to be the wheel. It is the spoke or bearing.
Check rim for cracks.
Spin the wheels, is it true side to side and up and down?
Loosen bolt, move the wheel a half inch, move it back. Tighten again. Sound goes away?
Completely remove the wheel. Spin the axle with your fingers? Feel a rough spot at every turn?
Tighten each spoke 1/8 turn. Naturally, mark them so you don't mess up? Feel anything funny? Loosen them again.
What I am saying is you can slowing eliminate the other causes leaving you with only the wheel and bearing. If you cannot fix those, it is time to call Rad maybe for another wheel replacement.