When you add a Gear-Pair, the background sketch and part-outlines turn on - which is most often inconvenient when you come to select the Dimension in the PArt-Editor.

However, if you really do need to turn them on, eg when adding Bevel Gears, then turn off the background sketches after Add Gear-Pair command is complete.

By the way, the term now (as is given in the Help and the Menus, for the 'other background stuff' is 'other kinematic and sketch elements'.