space roar?

"What was actually heard was something totally unexpected. Permeating the Universe was a strong radio hiss, about six times more powerful than anyone expected. No-one knew what it was or what was causing it. This was eventually christened "Space Roar" and remains one of the "Great Unsolved Problems in Physics"."
link

On my random walk through the interwebs I came across this article, which is low quality overall, but the space roar seems to be a real issue in radio astronomy - at least Wikipedia has an entry about it 8-).
I did not know about this "great unsolved problem in physics" until now, so please leave a comment if you happen to know more about it ...