Rachel’s tantalizing teases

The very name of the group Rachel’s seems to suggest an unresolved thought or story. And so does the Louisville ensemble’s music, stitching modern tonal classical styles with subtle, rock-distilled tension and well-integrated found-sound recordings into haunting compositions that seem like hints rather than complete statements.

Thursday at the Echo, the quintet highlighted pieces from its fifth album, “Systems/Layers,” a new collaboration with New York’s experimental SITI theater company.

Slow, sad figures from Christian Frederickson’s viola and Eve Miller’s cello gradually unfolded around Rachel (no, the group is not named for her) Grimes’ piano patterns, with Jason Nobel’s bass and Edward Grimes’ drums steadily lifting the music -- only for it all to melt away, notes hanging in the air, incomplete and yet engaging and entrancing.

Identified with the horribly named “post-rock” movement anchored by Montreal collective Godspeed You Black Emperor, Rachel’s finds a place between Sonic Youth and the somber spirituality of Estonian composer Arvo Part -- not really rock at all, save for general sensibilities.

The set perfectly capped an evening in which headliner and opening acts (singer-songwriter Matt Pond, in duet with Miller, and thrilling L.A. chamber-rock ensemble W.A.C.O.) all featured cello and none had an electric guitar.

That this took place in a rock club with an enthusiastic young audience is perhaps the real unfolding, unfinished story.