Noise inside, where does it come from?

[Supervinnie40]

I love my sweet 75. And I'm very pleased with how quiet and comfortable it is. But I do have to say that there is a big difference between driving at 50 km/h and 120 km/h.

Now, since the difference in noise is only really there when I drive harder, I am wondering if this tells me where it comes from?

MY guess is the wheelarch. I think the noise I'm hearing on the motorway is mostly tirenoise. Which gets inside the car via the wheelarch.

But 2 minds can think of more then 1 can. So perhaps you guys have some ideas where the added noise is coming from?
Is it mostly windnoise? Tirenoise? Or perhaps noise coming through via the bottom of the car?

[RogerHeinz57]

Hello, the road noise is really governed by only a few things, some tyres are more noisy than others, some road surfaces are really poor and contribute to harsh sounds, Not forgetting tyre pressures and tread design will play a big part in noise levels, other ideas are about sound insulation, my car has some additional insulation inside the boot, mainly behind the wheel arches where sat nav drives and pdc systems are fitted. These are large hollow areas that allow the road noise to be somewhat amplified. I have cured this on a budget by using carpet underlay sections rolled up and wedged into place. This works really well in my car. Some cars at the breakers yards I go to have a plastic air pillow type of packing plastic bags stuffed inside the hollow areas behind the back seat locking areas, my car has this too. The spare wheel area also has underlay foam around the edges together with emergency gear like hi vis vest, gloves and other bits and pieces. This all adds to the comfort and quietness of my car. The noise has been reduced nicely, may be worth a try.

[Supervinnie40]

Thanks for those tips John. I've been thinking about insulating some areas, but would first like to figure out where it comes from and if insulation at certain points actually makes a difference ;).

[roverbarmy]

If you need to fill an awkward area with insulation, push a large polythene bag into the area and use an expanding foam gun into the open end of the bag (you can wrap the open end around the nozzle with tape. The foam will fill the bag and the space, without the foam sticking to everything it touches (pain to get off without the bag trick). If you ever need to get it out, you can just dig the foam out as necessary and the bag/liner will eventually just pull away, leaving the area pristine. Remember that you may need some ventilation in some areas and that the foam is water resistant so may hold water/condensation.;)
Mike