“Furtive” is the best adjective to describe the sound of the xx. On their self- titled debut, the young London band conjures up the image of shy teenagers attempting to shag in her room while her parents stubbornly stay up, watching late-night TV. Their blend of the Passions’ angular post-punk and the hushed minimalism of Young Marble Giants — with small dashes of R&B — is undeniably sexy, but in a quiet, subdued way. Sounding like lovers carrying on an illicit conversation, Romy Madley Croft and Oliver Sim barely sing above a whisper as they trade off verses and choruses on tuneful tracks like “VCR,” “Crystalised” and the excellent “Islands,” which boasts such a can’t- miss hook that Shakira ended up covering it. Croft is also an engaging guitarist, adept at spinning out low-key guitar lines that sound like Will Sergent in an alley at 3 a.m. While the energy (such as it is) definitely flags on the back half of the album, xx is an intriguing, sexy and sometimes discomfiting debut — the musical equivalent of bedsprings squeaking in the next motel room.