This is the tool used for analyzing the noise from the catalytic converter. It is not used specifically for any of "our" cars but takes the place of ones ear I suppose. Van Gogh would like to have this I'm sure.
http://workshop-manuals.com/mercede...ust_system_catalytic_converter_noise_testing/
http://workshop-manuals.com/mercede...ust_system_catalytic_converter_noise_testing/