I used it to diagnose a funny noise on my car, by recording the ambient sound in the cabin with my phone - velcroed to the dashboard with its microphone pointing down at the gearbox tunnel - and announcing my speed when the noise was particularly pronounced.

Then I used sox to extract loud but low frequencies, and since I could hear it correlated with road speed I was able to verify that it was a particular bearing in the front propshaft by working out the relationship of frequency and gear ratio.

All without crawling underneath and getting oily!