Well, it depends on what kind of noice you're
experiencing....wind noise? Tyre noise? Are your tyres balanced and
wheels aligned? etc?
If you haven't serviced you car for a while, changing all the oils
may help a bit.
Tyres also contribute to noise, but there is no fixed indication
how often one should change tyres - there are km-ratings, but they
are just a rough guide.
If everything else is OK, the fastest and cheapest way to get rid
of the noise is.....increase the volume of your
hifi. 