[CraigFL]

It's my experience that cars that pop out of gear may not always be fully in gear. The first thing you need to do is to see if it goes into gear completely while the engine is stopped. If it doesn't, you may just need an adjustment of the shift linkage/cable. In any case, the rattle that stops when you press the clutch doesn't sound good. If you find that you can shift easily and completely into gear when the engine is off, and you can't when it's idling, then the clutch is probably not releasing.