The self-lveling suspension should not noticeable 'raise and lower' at times. As you add weight to the car, it will basically counter the loading to maintain a set height.

HOWEVER, when one of the airbags gets a pinhole leak in one of the folds, air can leak out. Park it on a kerb (or curb... ) and it may leak down overnight- then noticeably pump up in the AM.

As the airbags move around in their mounts, it is possible for a leak to come and go, so it doesnt do it all the time.

But you most likely need to replace the airbags. Pretty cheap, 30 minute job- easy. Search for DIYs and posts about it. US$150 for parts? as I recall

My guess...I dont have it on mine.