20 questions (well maybe not 20)
When did it start?
Did you just buy new tires and you have a loose wheel nut? (pretty obvious, but _ _it happens)
How many miles (kilometers) on the clock?
What has been done to it lately? any service? any bumps? any disgruntled girlfriends?
Is the noise coming from the front or back? driver side or passenger side?
Does it make the noise turning the other direction?
Does the noise frequency change with speed?
Does it make the noise only at low speed or only at high speed (cornering hard?)? when cold (just started, or after many miles, or all of the time?
Sitting still, either with the engine on or off, can you bounce the car and make the same noise?
Do you have a friend that is willing to be strapped onto the bonnet or boot to help locate the noise? JUST JOKING! DON'T TRY THIS AT HOME!!
Have you had the car on a lift to see if anything is about to fall off?
Good luck. Let us know what happens.