The applicability of the magnetic resonance sounding (MRS) technique in urbanized areas is limited by the inherently weak signal from the subsurface water which is often deeply buried in noise from anthropogenic sources. The noise can have spatially variations on even sub-100 m scales and the signal to noise ratio of an MRS measurement can therefore be optimized by a careful choice of the exact location. In this paper we present an instrument for fast mapping and analysis of the noise conditions at a site prior to MRS experiments. The main components of the instrument are two induction receiver coils connected to amplifiers and a digital oscilloscope controlled by a PC. Analysis of the gathered data reveals the spatial distribution of the different noise components, in particular powerline harmonics and spikes. A comprehensive noise map of a test site is presented and analyzed.