A blogger who recently visited the Philadelphia Museum of Art was struck by Duchamp’s "assisted" readymades — effectively assemblages — and in particular the 1916 With Hidden Noise. Sadly the object can no longer be shaken, which makes its title (and the secret noisemaker inside) both poignant and especially compelling. The "noise" is now hidden in the museum forever; it cannot be heard as such, but lurks like an infrathin ghost…or else you can hear it here.