Clicking sound when taking off from a stop

[guitar guru]

When I let out the clutch to get going from a stoplight, I hear a kind of click-almost grinding-sound possibly coming from the gearbox. It only happens when engaging first or second gear, and there is no such sound when I'm cruising. It's as if the gears are having trouble meshing, or maybe there is slack in the chain or something. Any ideas? I think it's getting more prominent too, so I wanna figure out what it is.