My 12-year-old Prius V hybrid makes a loud rattling sound when I start the car and then when I accelerate. It does go away after driving awhile.
The Toyota dealer has said that it is because the car is switching from EV to gasoline engine mode. Is this normal? Is there a way to get rid of the rattle? People on the street can hear it!
Thank you for your help.
— Jane
Well, I’ll give you two answers, Jane: a happy answer and a sad answer.
The sad answer is that you could have a leaky head gasket. That could make your gasoline engine run rough at first. And a rough-running engine will make everything around it rattle.
That would be sad, indeed, especially for your bank account. But I don’t think that’s what’s going on. It’s more likely that the noise is coming from your exhaust system.
All gas-powered cars have catalytic converters. And because those converters get red hot, each one has a heat shield around it — top and bottom. The heat shield is just a thin sheet of metal mounted a few centimeters away from the converter itself.
It’s there to prevent you from setting your car on fire if you park over some tall grass or a pile of dried leaves. Although a fire would definitely solve your rattle problem, Jane.
Anyway, as cars get older — and your 12-year-old Prius qualifies — the rivets that hold the heat shield in place can fail or corrode. When that happens, that thin sheet of metal will vibrate — against the converter itself or whatever it used to be attached to. That causes — what? — a buzzing or rattling sound.
And as the metal parts heat up, they expand and touch each other, and that often causes the rattle to stop after you’ve been driving a while. But it’ll always be most noticeable when you start the car first thing in the morning, when everything is cold.
If it’s not the heat shield, another part of the exhaust system could behave the same way. If you have a broken exhaust hanger, for instance, that could also allow the exhaust pipe to rattle against the undercarriage, especially when the car is cold.
So, I’d leave the car with your mechanic overnight. If he starts it when it’s ice-cold, he’ll hear the rattle. And he’ll know instantly whether it’s an engine noise or an exhaust noise.
If he sends you flowers and a card, you’ll know it’s not an exhaust noise. Good luck, Jane.
