i am considering doing my 3rd year project on making a det sensor (u know a knocklink)

now what i want to know is what does a car thats detting sound like

is it like this http://users.wpi.edu/~mark944/neste.../knockstuff.htm
(go half way donwn the page and click on sound file)

or is that just the background noise?

ive bin told it sounds like tinfoil but that doesnt sound like it.