Car buzzing when off for over 48 hours
April 19, 2020 9:56 PM   Subscribe

My Subaru Crosstrek had a moderately loud buzzing sound coming from underneath it tonight. It hadn’t been driven or even started in over 48 hours. Starting it made the noise stop immediately. Ideas?

The buzzing appeared to be coming from near the rear of the car and definitely underneath (Much more audible underneath). Almost sounded like an electric toothbrush rattling in a pipe but quieter (if that makes sense). I did pop the hood while the noise was going and no noise appeared to come from from there I could identify.

No history of car trouble - gasoline model (no batteries or power cells that could have electrical hum). The car was parked on a flat solid concrete pad outside my house with no sources of vibration nearby. Very still windless night in a super quiet neighborhood with no traffic within a few thousand feet. This was well after dark and on a cool night (low 40’s). Car started fine - no warning lights - and the noise stopped immediately. Honestly my best guess was an insect trapped in the muffler and vibrating the pipe. But the noise seemed too consistent and went on for a few minutes without pausing while I scratched my head trying to find the source.
posted by inflatablekiwi to Travel & Transportation (3 answers total)
 
Best answer: That's normal. The fuel pump runs an evap test when the car's been sitting for a while and will throw a check engine light on next startup if it detects anything amiss.
posted by Floydd at 2:41 AM on April 20, 2020 [3 favorites]


Our Toyota does the same thing.
posted by LoveHam at 4:39 AM on April 20, 2020


Response by poster: Ahh excellent - thanks Floydd - that will be exactly it! Mrs Inflatablekiwi even reminded me this morningshe’d taken the car yesterday afternoon or a few minutes to go pick up the mail - so it checks out that it would run 5 or so hours after the car was last on.

It was such a quiet night it must have been the first time I could hear it properly without background noise.
posted by inflatablekiwi at 5:23 AM on April 20, 2020


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