[Lingo] いつからか

[s smith <sjs@example.com>]

Hi all.

I'm trying to understand the lyrics _Far_Away_ sung by Ayumi Hamazaki.  My problem is around the 「か」 following いつから.  I think I understand いつから.  I've seen this before and a search on the web shows　「いつからか」 to be fairly common on the web.  What is か doing here?

The segment with it's translation is below:

そして いつからか忘れてた景色達 探しながら
And while searching for that place I had forgotten for so long,
聞こえる波音が何だか優しくて
the sound of the waves were somehow soothing;

Thank you
Steve Smith