LC filter before analog pin of microcontroller
I used CircuitLab to plot the frequency response of the filter. I don't like it very much. Any noise at 10.5 kHz will hardly be filtered at all. It will filter fairly well above 15kHz. So, if that is where your noise is, this filter is OK. If your noise is lower than that, you should use a Sallen-Key butterworth filter.

Or, if you show your entire circuit, there might be better solutions. For example, if your input is always 400 Hz, you could bandpass the AC before you rectify it.







simulate this circuit &ndash; Schematic created using CircuitLab



Edit: An alternative inspired by Autistic's answer. Add a 33 ohm in series with L1 to dampen it. You should subtract any resistance in L1 if it is significant.