"
Kangaesugi no messeiji
Dare ni mo todoku kamo shirenai de
"Thinking about a thing I heard just the other day, but it hasn't gone away"
The thing that Miku/Gumi is talking about here, is something that was said about them or someone else, like a rumor of sorts. The reason it hasn't gone away is that rumors tend to stick around for a while and continue to hurt people for a long time after they're started.