I have multiple segments of data that look similar to the one in the image:

Decay

In the signal there is some stability, then some period where the signal is decreasing, and then the signal stabilizes again. I am trying to find a way to identify the intervals where the data is generally decreasing (the area between the red lines in the image), but the noise in the data has made this difficult for me.

I have tried using variance and a comparison of a simple moving average and exponential weighted moving average to find the points at which the decrease begins and ends, but the noise is messing things up, so my main questions are for any recommendations for a good way to smooth out the noise or even better if there are any suggestions on how to identify those decreasing intervals.