I wish I could point to just one issue and say "this is it" but when you are dealing with the rear suspension or rear end are too many potential candidates to look at. For example, have you had the rear shocks checked? It might be the bushing at the top or it might be that the nuts and bolts at the top and bottom need adjustment. Or it could be that the exhaust system is loose and banging against the body. It also might be a loose rear suspension member that is banging against its carrier. Or, it could be something as simple as flat-spotting on your Jazz's rear tires. So, what do I think it is? I am tempted to say it is likely related to a loose bushing on one of your Jazz's shocks. The bushing is a hard-rubber piece at the top of the shock. If it is loose, it could be banging against the cover and creating the sound you hear. If you feel competent to check this problem, you will need a good pneumatic jack to lift the rear end and keep it up safely. Never use the scissors jack that came with your Jazz because it is not designed to keep your vehicle in the air so you can work on it. Use it only when you are changing tires. This is a problem that should be addressed when you have time as it should not affect your car's handling. It is more of an annoyance than anything else. To see if there might be other issues affecting you Jazz, look at http://www.safecar.info.