We report the tentative detection of the modulation of a transient, redshifted Fe K emission feature in the X-ray spectrum of the Seyfert galaxy NGC3516. The detection of the spectral feature at 6.1 keV, in addition to a stable 6.4 keV line, has been reported previously. We find on re-analysing the XMM-Newton data that the feature varies systematically in flux at intervals of 25 ks. The peak moves in energy between 5.7 keV and 6.5 keV in each sequence. The spectral evolution of the feature agrees with Fe K emission arising from a spot on the accretion disc, illuminated by a corotating flare located at a radius of (7-16)rg, modulated by Doppler and gravitational effects as the flare orbits around the black hole. Combining the orbital time and the location of the orbiting flare, the mass of the central hole is estimated to be (1-5)e+7Msun, which is in agreement with values obtained from other techniques.