Both speakers are doing this with no cables connected? If so that seems unusual. Bad power? Maybe try a different outlet, or if using one, a different power bar.
Check this link and scroll down to the mp3 example that sounds similar to yours. Maybe you had a power surge cause damage to both speakers?
’ I found a post on the Cakewalk forums
from a gentleman with the same issue from a KRK Rockit 6 that turned out to be filter caps in the power supply which caused damage to related resistors. He was thoughtful enough to include the link below to an mp3 of the crackle."