Tightening up the slack on your garage door will allow it to run more efficiently and will prevent loud noises that disrupt your home.
Garage door chain loose when closed.
Once you are clear that the only problem is a slightly loose chain then you can begin fixing the problem.
Over time though this slack can increase or the gear and sprocket assembly can wear and the chain may pop off the sprockets.
Chain driven garage door openers should have some slack in the chain for optimal performance.
Step 2 turning off the power.
If in doubt replace the chain completely.
You can put the chain back on your automatic garage door opener using a simple adjustment mechanism.
Make sure that the garage door is closed and that you have another way of getting out of the garage.