I live in a ten-story condominium building that has two wings, and is roughly shaped like a wide "V". The open part of the "V" faces a concrete parking structure.
Now and then, the local carpet cleaning service will park their bright yellow vans between the open "V" and the parking garage, run their long hoses to the unit they are cleanng, and start up the carpet cleaning machine, which is located in the van.
When this happens, the most wonderful drone ensues and continues until the job is done.
This recording is comprised entirely of sounds recorded during a three minute period as I walked from my condominium, through the lobby, past the cleaning van, and into the garage. The recording also caught the sound of some conversation between me and my wife as we walked.
Several copies of the recording were layered, some reversed and some stretched.