We report on joint SUMER and TRACE observations of a transient event which occurred in a cold loop, lasting a few minutes. The measurements were taken on 1999 June 3 between 09:18 UT and 11:08 UT. A sequence of TRACE images in the 1550 Å and 171 A filters show a disturbance which originates at one foot-point and propagates along the loop. The SUMER slit is placed at the other foot-point of the loop. During the event an intensity increase and a red shift of about 30 km s-1 was detected in the N V 1238.82 Å line. ID numerical simulations are performed and observable quantities derived from the results of the simulations. The observed dynamic behaviour of the N V 1238.82 Å line profiles is recovered. These results suggest that the observations could be interpreted in terms of a short-lived siphon flow reaching a speed of 110 km s-1 and driven by a nonlinear heating pulse. The energies required to drive the observed red-shifts are estimated to be 1024 erg. The absence of a significant blueshift caused by the return flow is explained.