In my lab we are beginning to do neural recordings which are very sensitive to noise... given the fact that signals are just few microvolts. In addition we are consistently observing nice spikes in the 50Hz signal picked up by the amplifier! They are very periodic in fact (once every 10ms) and each such spike lasts about 1ms and they are phase locked to the 50Hz sine! We realised that it is there in the line voltage but not rectified by the UPS somehow... Is there any solution?? Any front-end equipment (economically priced and easily available) that will rectify the power supply for the entire lab?