We can go into some zoos and think, this is delightfully quiet - but it might be that some animals don't think it's quiet at all, because urban areas have a lot of chronic infrasound," said lead researcher Suzi Wiseman.
Ms Wiseman, who has just completed a doctorate in environmental geography at Texas State University, presented her preliminary results at a meeting of the Acoustical Society of America in Indianapolis.
'Healthy soundscape'
Rhinos, she explained, can hear down to a frequency of four hertz, whereas even a human baby, with entirely undamaged ears, can normally only pick up sounds as low as 20 hertz. Giraffes and elephants can also hear in this infrasound range.
The other end of rhino hearing might also be quite acute, because people have witnessed the animals making high-pitched whistling and giggling noises when adults and youngsters play.
"The soundscape is something that zoos need to consider and it's something that can be improved," Ms Wiseman told the BBC.
She said that although zoos and other institutions had made a lot of effort to make their animals as comfortable as possible, "nobody's really looked at the noise factor".