On my 420 on warmer days (only when the cars is cold), the car whistles for 2-3 minutes and the sound goes away for the day. Tech said nothing serious, just the air filter.

IS this something that I should be concerned and why does it not occur on my 300 or any other Benz? Should I just replace the air filter? Should be cheap, right? The noise is just annoying and on some days can be loud.

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)