Dear Car Talk:
I have a 2011 Toyota RAV4 with about 95,000 miles on it. Recently, I noticed that when I get to about 40 mph, the car makes a weird rattling or loudish whirring sound.
It sounds like it is coming from just in front of the front seat area of the car. If I hit the gas hard or take my foot off the gas, the noise stops.
I'm hoping you can help me figure this out. I tried taking it to a mechanic, but since they aren't getting an error message on their computer, they don't know what it could be. Thank you! -- Edie
You've given me several excellent hints here, Edie. If only I was smart enough to make sense of them.
Actually, I think your noise is related to the exhaust system. My first guess would be that a heat shield around your catalytic converter is loose and that's what's rattling. Why do I think that? Well, first, since there's no warning light or computer code, that suggests to me that it's not an engine issue.
Second, rattling exhaust systems are often sympathetic vibrations. That doesn't mean they feel sorry for you when they vibrate. It means that they vibrate because something nearby is vibrating at just the right frequency to set them off. And these sympathetic vibrations in cars often happen only at specific speeds.
Third, your catalytic converter is located just in front of the passenger seat, under the car -- right where you say the noise is coming from. It's possible that it's not the converter's heat shields. It could be a loose or broken honeycomb inside the converter or some other part of the exhaust system has come loose or is touching something it shouldn't be. But the heat shields are the first thing I'd look at because that's very common.
If you can get your mechanic interested enough, I'd strongly suggest he take a test drive with you and hear the noise for himself. First, it'll allow him to rule out anything dangerous. Second, once he hears the noise and where it's coming from, he'll probably know exactly what to do.
If he can't identify it during a test drive, he can always put the car up on the lift while someone else stays inside it. The driver can then rev the engine to different speeds and try to make the noise occur. If they can get it to make the noise on the lift, the mechanic under the car should be able to find the cause in a matter of seconds.
Even if he can't duplicate the noise, he may be able to find something under the car that's obviously loose or not connected as it should be. And if he fixes that, there's a good chance that'll make the noise go away ... along with a few bucks from your bank account. Good luck, Edie.
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