New to CNC, LinuxCNC and Gcode. Unwanted axis movement

Hi all
I Have a problem you might be able to help with, I don't know if it's a Gecko, LinuxCNC or my brain.

If I enter a simple straight line command to the mill ( G1 X580 Y0 F100 )then I find the other axis (Y in this case) will also move, very slowly, but also gradually "drift" in the negative movement. So the straight line becomes angled.

If I change the code to G1 Y580 Y0 F100, then the X axis will negatively drift.
No unwanted drift on the Z axis.
A circle generated in Rhino and then converted to Gcode using "DXF2GCODE" will mill beautifully, and end up at the same point it starts.

I tried to "reset" the code by adding....
G21 (Units in millimeters)
G90 (Absolute programming)
G64 (Default cutting)
G17 (XY plane)
G40 (Cancel radius comp.)
G49 (Cancel length comp.)
G61 (exact path mode)
G94 (mm per minute feed)
G54 (co-ordinate system)
G80 (cancel canned cycles)
M2
to the start of that simple straight line code, but if anything the drift is worse.

I'm running LinuxCNC to a Gecko G540, gantry type mill with 2 y steppers, one X and one Z stepper.

Jim

Seems it's fixed itself.

*shrug*

Yeah, a bit of rogue code stuck in there.

All good now.