I can't address the crackling sounds but can understand the relapse or crash.

Having a few good weeks does not make a recovery. Returning to old activities and behaviors should be done carefully with a slow return to intensity.

Try to let go of your past abilities. Then, you can define and accept your current limitations and slowly try to stretch your abilities. Recovery is not a single point in time. The brain slowly develops tolerance for different functions and activities.

We need to return to these past functions and activities slowly and one by one. We need to also allow time after adding past functions to our daily efforts. The relapse from doing too much too fast usually come the day after the effort.

Just because we did not crash or relapse during the effort does not mean we have regained the ability to out out that effort. We need to avoid jumping into deep water when we have had good days on the beach. Try the wading pool first and wait to see how our brain reacts.

Most of us have learned this lesson the hard way, we pushed to hard in our initial attempt to return to 'normal' activities. Our new normal may be quite different than our past normal.

My best to you as your regain your strength.