It sounds like you have a bad switch that makes the spark come on. They are located on the shaft of the gas valve.
It is item number 4 in this picture.
Click Here for Picture
There is one for the left and one for the right side. You can try disconnecting each one and see if it stops and that would narrow it done to which one is bad.
They only run about 15.00 each, and can be purchased at your local parts store.
right side is part # XXXXX
left side is part # XXXXX
They are behind the control panel.
Control Panel Assembly Removal
1. Remove power from unit.
2. Remove burner switch control knobs.
3. Remove front screws securing control panel to
4. Remove screws located on the left and right sides of
the control panel.
5. Grasp control panel on the far left and right sides and
gently pull the control panel out and down.
NOTE: The electronic control located in the control
panel is a sensitive item, handle gently.