The city, the country & me: unidentified noise

actually I wanted to make a recording of the small eschbach river, but when I kneeled down to find a good position for the recorder on the floor, I heard this droning noise (I don´t know what it is, perhaps a drainpipe?) and the noise of the river was on ground level no longer present. the place was covered by leaves and when I brushed them aside there was only asphalt. i will check it out in near future. in the background you hear sometimes cars passing by. the city, the country & me: november 2, 2009