Weird sound on newer GE's

[emd_SD_60]

Whenever I am watching/videotaping a train on the UP, if it's led by a newer EMD or GE, as the locomotives pass by I always hear a continuous "psst psst" sound from them. Does this have something to do with the air braking system? (and yes, I tried Google, but no results to my satisfaction. )

[cb&q bob]

What you are probably hearing are the automatic reservoir drains. Some of these recieve an electrical signal to open periodically, usually when the air compressor cycles on and off, and drain condensation from the air tanks but most of the drains on UP locomotives work without any electrical power except for a small heating element to keep them from freezing. Depending on the amount of moisture in the tank and the condition of the valve, some of these auto drains pop almost continuously and sound alot like an old lawnmower engine with a bad muffler.