Steel-spring floating-slab (SSFS) has been widely used in track structure because of its effective vibration isolation. The energy transferred to the foundation is significantly reduced. Usually, the frequencies are low in the course of analyzing the vibration of a floating slab. When considering the vibration isolation effect of SSFS, the mass of spiral spring and its detailed structure in the supports is usually ignored. This assumption will cause errors in the high frequency vibration characteristics. In fact, there is certain mass in the supports of floating slab. In addition, when the diameter of spring is equal to integer times of a halfelastic wave in it, the wave effect can be produced in the supports. At this time, the standing wave effect in the spiral springs should not be ignored. Based on the linear assumption and using the four-end parameter analysis method, we get the range of frequency that is caused by the wave effect. Three groups of noise in a carriage of an actual running vehicle are measured. In addition, it is explained why the noise is higher when the vehicle is running over an SSFS zone, compared with the common track. Some suggestions are put forward that will reduce the low frequency noise in the urban transit carriage.