That wasn't TCAS. TCAS RA's are inhibited below 900' on landing. It was probably the ground-proximity warning system (GPWS) and the alert you heard was likely, "Sink Rate" or, "Glideslope". It's not unusual to get one of those from momentarily exceeding the programmed stabilized approach criteria. Can also be caused by flying over rapidly rising terrain on short final or ground vehicles interfering with the glideslope signal on days with good visibility.