The authors examine the problem of diffusion over a fluctuating barrier in the limit where the barrier fluctuations are extremely fast compared with all other timescales in the problem. In the white noise limit, the decay of probability from the metastable state is exponential with a characteristic timescale exhibiting Arrhenius behaviour. For small but finite correlation times for the fluctuating part of the potential, the effective barrier increases with the correlation time. Implications for liquids above the glass transition are discussed.