So I’m driving home today, and I start to hear a hissing noise from the passenger air vent. At first I’m thinking it’s liquid condensed from the AC sloshing around inside the dashboard (drain hole clogged up maybe).

But the noise doesn’t seem affected by turning, or speed. I try turning the AC on and off, then the fan itself. Nothing. Even with the climate control turned completely off, I’m still hearing this hissing. It’s more or less constant, and occasionally sounds “wet”, like a leaking hose that periodically gets into water.

I’m going mad on the drive home trying to diagnose it — turning things on and off, braking hard, turning, etc. Only thing that affects it is when I brake sharply; when the nose dives and the car’s plane becomes angled forward for a moment. The hissing stops briefly, then resumes.

Finally I get home in the garage where I can check it out better. Still hissing even when I turn the ignition off. I’m wondering if it’s a leaking hose, a freon leak or something. But there’s no unusual smell.

So I duck my head in on the passenger side to hear better exactly where the sound is coming from, and…

…it’s my bottle of Dr. Pepper in the front seat, hissing because I didn’t screw the cap on tight enough.

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