I hadn't heard this until today.
"In December 1966, Warhol and David Dalton designed Issue 3 of the multimedia Aspen. Included in this issue of the magazine, which retailed at $4 per copy and was packaged in a hinged box designed to look like Fab laundry detergent, were various leaflets and booklets, one of which was a commentary on rock and roll by Lou Reed, another an EPI promotional newspaper. Also enclosed was a 2-sided flexi disk, side one produced by Peter Walker, a musical associate of Timothy Leary, and side two titled 'Loop', credited to the Velvet Underground but actually recorded by Cale alone. 'Loop', a recording solely of pulsating audio feedback culminating in a locked groove, was 'a precursor to [Reed's] Metal Machine Music, say Velvets archivists M.C. Kostek and Phil Milstein in the book, The Velvet Underground Companion. 'Loop' also predates much industrial music as well. More significantly, from a retail standpoint, 'Loop' was the group's first commercially available recording as the Velvet Underground."