Extruder stepper running backwards before first layer.

[ALTTAHX]

I have just finished constructing and calibrating my Rostock Max V2, it heats, moves, extrudes perfectly under manual control but when I come to print the fan shrouds the stepper for the extruder runs backwards at high speed for a couple of seconds before starting to run forwards at a normal speed when the head comes down to print the first layer. Obviously this removes the filament from the print head and the first layer or 2 are not printed so I cancelled the jobs.
Any ideas?

[ALTTAHX]

Looking through the Gcode for the print there is this near the beginning: G1 F6600 E0
Could this be extruding at high speed backwards from a pre-set extruder setting (something above 0)?

[JFettig]

Is there a G92 E0 in there right before that line?

What slicer are you using? Can you stick that into some "start code" area of the slicer?

[ALTTAHX]

Yes there is a G92 E0 before the code I pasted in.