I think its the shockers..mine makes the same sound ngek3x...for klong3x sound, do check whatever u have inside yr boot space..could it be yr spare tyre or sth else..thats from my experience la...normally the long shaft will cause the car vibrate at certain speed..its quite expensive but rarely people replace them unless it bends..might be useful info, but let other big sifus have to say...cheers