A Loose Heat Shield May Be Your Noisy Rattle

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Avoiding Muffler Repair: Troubleshooting the Problem

Woman lying underneath car, holding tools
Slide under the car to inspect for your rattle. MECKY/Photographer's Choice/Getty Images

A loose heat shield can sound like a tin can full of rocks, very annoying. How do you know if your rattle is a loose heat shield underneath your car to truck? The easiest way to do it is to slither underneath your vehicle and start shaking things until you find something loose. There should really never be a loose part underneath your car or truck. Loose parts almost always lead to repair bills. If you can catch something as simple as a loose exhaust heat shield early, you'll avoid not only the charge a muffler shop would hand you for tightening one or two bolts, but you may potentially avoid paying to have an expensive factory heat shield replaced. Those things can run into the hundreds of dollars! So climb under there (when the engine is very cool, like before you drive it on a weekend morning) and start looking for loose stuff. It can help to have somebody listen for you while the engine is running. If you don't hear it at first, rev the engine slightly. Some loose shields have to hit their perfect harmonic frequency to launch into a full rattle. If it looks like a loose heat shield is what's causing your rattles, read on to pinpoint the source and fix it free. 

Wait until your car is nice and cool, at least an hour since it was last driven, muffler repair on a hot muffler is no fun. Raise the car and safely secure it on jackstands. Now you can shimmy underneath to see what's going on.

About two feet behind the engine you'll see the exhaust pipe heading toward the back of the car. Right about where your seats sit, there will be a thin metal shield between the exhaust pipe and the floor of the car. Pull, push, poke and prod this every way you can imagine -- you're trying to make it rattle. If it's loose, you'll hear the same irritating sound you've been hearing.

If you can't make it rattle, you'll have to start the car. I highly recommend that you do not crawl underneath your car while the engine is running. Instead, poke your head down there and listen closely to see where the rattle is coming from.

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Avoiding Muffler Repair: Shutting It Up

Tighten the heat shield to shut it up.
TIghten the heat shield bolts. photo mw

If you've found that the heat shield is loose, all you need to do is tighten it up. With the engine off, crawl under the raised car and tighten all of the bolts holding the heat shield in place.

You may also find that the heat shield has been bent by something it hit in the road. You can bend it back using pliers or a screwdriver (even a hammer if you're careful), all you have to do is pull the shield away from any place it might be touching the exhaust pipe. Now is when I will tell you again that your vehicle needs to be before you get under it! Be sure the car is in Park, the emergency brake is on, the wheels are chocked by something strong (like a real wheel chock). Better yet, try to do this repair without jacking the vehicle up at all. I know this isn't always possible, but it's much safer if it's a possibility.  While you're under there banging and pushing, be careful not to damage the one thing under there that's fragile -- the oxygen sensor. They stick out in various locations along the exhaust system, in front of the catalytic converter. One bang with a hammer and you might have wasted $300 replacing an O2 sensor!

Finally, if the heat shield isn't the culprit, you might have a broken exhaust hanger. A broken rubber exhaust hanger is another job that is almost free (not quite) and can save you a bundle of money if you decide to tackle it yourself. You'll see this during your inspection, and should check it if your muffler seems to be hanging too low these days.