Indeed, the closest things I've been able to find have been these two studies [0, 1] which investigate a large number of different possible incidental stimuli (from lights all the way to the placement of the assistants during the experiment). Neither of these mention sand as far as I can tell nor were they written by a "Young". There is a paper that does, though, found here [2], which used it in the walls of the maze, but it does not mention a reason for doing this.

For fun, I also found this 1938 paper as I was looking around that I haven't read. It's interesting what random things scientists were doing during this time and what debates were had [3].

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[0] "The effect of incidental stimuli on maze learning with the white rat" https://doi.org/10.1037/h0071189

[1] "Further studies of the effect of incidental stimuli on maze learning with the white rat" https://doi.org/10.1037/h0075810

[2] "Correlations between conditioning and maze learning in the white rat" https://doi.org/10.1037/h0053662

[3] "The effect of a native Mexican diet on learning and reasoning in white rats" https://doi.org/10.1037/h0061906 (The study found that the rats had less body mass, but did not find a statistically significant difference in maze solving ability.)