Does the noise change in pitch between those two speeds or stay constant? Can only be something to do with the running gear since it's road speed dependent I guess...

 

have a look at the rear prop shaft centre bearing and its supporting rubber mount

 

When you say decelerating, do you mean coasting or under engine braking? Is the noise still there above 40 kmh but it is drowned out by road and wind noise? I've had something similar and mechanic has diagnosed a loose baffle in the exhaust box, which gives off a metallic whining kind of sound, but it is intermittent, not constant and disappears under deceleration (just updated an entry on it). Just a thought. Try banging all over the silencer box and seeing if you can replicate it.

 

Thanks for the responses.

Calumski -The noise does not change in pitch. That’swhat I was thinking too. Thanks mate

Rgh0 - that sounds like a solid guess. Thanks, I’ll look into this more and will let you know.

Whippetboy - something exhaust related was my first guess but it happens with deceleration and coasting, and revving through it so I don’t think this is it. Thanks for yourresponse though mate 👍

 

On mine a section of the metal exhaust heat shield underneath was slightly bent and it vibrated & caused a noise but only at a certain engine speed. All I did was bend it back into position and the noise vanished.

 

If only all repairs were that easy and cheap! Thanks for the tip capese21

 

Record the noise and post it on here, like a picture speaks a thousand words sound does to.

Other posts with similar odd noises was the exhaust baffles. Go underneath with a hide mallet and give the silencer a whack. See if the noise can be heard.

 

Handbrake brake shoes worn out