Distortions in TPC data (track residuals) are seen in 2004-2006 data which are hypothesized to come from a floating Gating Grid wire. Notes from a meeting of TPC experts regarding the topic held in October 2006 can be found here.

See PPT attachment for simulations of floating grid wires from Nikolai Smirnov which show that the data is consistent with two floating -190V wires in sector 8, and two floating -40V wires in sector 3 (all wires are at -115V when the grid is "open").