A moving average may generate an irregular oscillation even if none exists in the original data.
Slutzky-Yule Effect
See also
Moving AverageExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Slutzky-Yule Effect." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Slutzky-YuleEffect.html