It is so weird. Which is what makes it super cool and awesome, and you should totally do it every time.
I would do it!
I currently own a 1989 Kawasaki KZ-P it's probably one of the most popular police motorcycles in the USA it makes it's own distinct sort of quiet sound which I love.
Having owned Harley's in the past I could see how those who ride the wanna be a harley's might want to copy the sounds of a real harley...
I have hummed the tune to CHIPS while riding my KZ and have been more than once mistaken for a cop..
If you have a Harley, you won't need to make the sounds! Harley-Davidson has a bonafide patent on their sound!!