Joke exhaust whistles - far0n
Anyone else used one for a practical joke ? Fitted one to my mates car the other day. He drives out of work with his car sounding like an old style kettle !!! The 30 mile journey back to Bishop Auckland must have seemed like an eternity. Funny thing was he rang his mate who was a mechanic and described the symptoms. The mechanic said "..sounds like you need a new catalyst". My mate was actually quite relieved when I took the little insert out of his exhaust pipe. Apparently I saved him £400 !
Joke exhaust whistles - Mapmaker
& when your mate is pulled by the police (Murphy's law ways that the one patrol car in Britain happens to see him) and is then done for unroadworthy car or whatever - or if nothing else is held over for half an hour, misses picking his son up from school etc. etc., then he will be an ex-mate.

Potentially not funny. Very much so.
Joke exhaust whistles - THe Growler
They are a pestilence. Every darn jeepney in Manila has one. There are an estimated 27,000 legal jeepneys in Metro and probably half as many again illegal. If you imagine these rattletraps stop on average about every 100m to pick up/put down passengers (every slowdown sets off a whistle, a bird call, a croaking frog, you name it)......need I go on.