The superscription to Psalm 7 seems to be universally interpreted as refering to an event in David's life. "'al divrey kush" is translated as "concerning the words of Cush" (or recently, "wegen der Angelegenheiten betreffend Kusch"). Way back in 1971, however, Childs proposed another interpretation, which seems to be consistently ignored (in "Psalm Titles and Midrashic Exegesis"). He has the following to say:
"In my opinion, this interpretation is mistaken. Every other example of the use of >'al< in the Psalm titles refers to the manner in which the Psalm is to be rendered and never to a historical referent. The preposition rather indicates that Ps. vii is to be sung "according to the words of Cush" (cf. the parallel in Ps. lxii) and belongs to a liturgical setting."
No commentary takes this up, and simply assumes it to refer to an extra-canonical historical tradition. Childs' interpretation seems plausible to me (especially because of the parallel with Ps 62). The LXX translates Cush as chousi - the Nubian - which >does< give it a Biblical anchor in 2 Sam 18:31 (according to Terrien). But this would seem to me to confirm that the original was liturgical and the LXX struggled to interpret it, so it gave it an inner-Biblical referent in order to make sense of it.
Philip Sumpter