Low frequency sound on Prius 2009 when ghoing over small bumps.

I have also heard an exaggerated sound when going over rough roads. Sort of like what I'd hear in other cars going over a bridge with a metal grid for the deck, except much deeper and more ominous. Scared me that something was wrong with the car at first.

 

It is because of the hatchback. Your cabin is connected with trunk.

 

Mosbat:

Have you tried taking a mechanic with you for a test drive? Then you could point out the noise to them.

 

I have noticed a similar sound on my 2009 as well. It started some 6 months after I purchased it and is now frequent and annoying. It sounds like a low frequency beeping sound to me, and occurs more when I drive over the slightest bump or gravel driveway. It however doesn't seam to happen when the car is off and parked, but can happen at a stop while running.

I took it to the dealership and all they said was they couldn't recreate the noise. And said it might be something else that is normal. Not hearing it for the first 6 months I don't believe it to be normal. Whatever it is, is covered under warranty and I will again bring it up next time I am in for a oil change.

 

Dear David,

We have exactly this problem with the 2009 (package 4) Prius we bought just over a week ago. We also hear the low frequency "booming" sound when we go over small bumps in the road, or when there are vibrations. It seems as if the shape and structure of the car's cabin is amplifying normal road noise. It's driving me pretty crazy, actually. It gives me an earache and my wife a headache after a while. We brought the car back to the dealer and had the mechanics look at it. They didn't think anything was wrong after test driving it with me as I pointed out the sound, and after keeping it overnight. Could it be that some people are more sensitive to this sound than others?

I went online and found a company called "LMS Engineering Innovation." They apparently gave a powerpoint presentation titled "NVH (Noise Vibration and Harshness) of Alternatively Powered Vehicles" some time ago at a conference in Istanbul. In the presentation, they talked about their research on a Prius (and a bus). They said that "cross over effect on orders leads to amplification of vibration noise" and that "low frequency domain critical." I don't know what this all means, but I wonder if the shape and composition of the car's cabin, along with the particulars of the engine, cause this problem we are observing.

In your research, did you find any ideas for a solution? What did your mechanic say?

Important fact: We test drove another 2009 Prius (a lower model) and didn't hear the same effect. There was some low frequency sound, but it was not overwhelming as it is in our Prius.

Keep in touch,
Malcolm

 

Hello David, Mike, and Malcom:

You might try checking out the hidden storage well under the rear cargo mat. The tray on my 2009 has some molded in spaces for the lug nut wrench, tow hook, etc. These could be loose and bumping around.

Even more likely could be the spare tire itself. Remove the storage well to access the spare. Make certain that it and the jack are secured properly, and that none of the sound insulating foam has moved. While you're at it, you might want to check your spare tire pressure. If the tire pressure had decreased, the tire size could have shrunk, resulting in the tire bumping around.

Another thing to check is the 12v battery. Be certain that it is secured properly.

As has been mentioned, the cargo area can resonate into the passenger compartment. So the cargo area itself should be check out thoroughly. It might help to have someone sit in the back seat while you try to recreate the conditions that are causing the sound. Then they may be able to help you locate the source.

Finally, you might want to check the muffler. If it got hit at some point, it may have moved up into a wrong angle, such that it is hitting something on the body when going over bumps. It should hang freely without hitting anything.

Let us know if you should get this problem resolved. I don't notice this problem on my package 5, nor on some lower level 2009's that I've rented recently.

 

I tracked down a rattle that appeared when I hit certain vibrations (different road surfaces). Not sure it was a 'boom' but it had different noises at different times.

I finally nailed it. It was the back sun shade rack. Where it rests in the side holder slots. There is some pretty chinzy black rubber padding on the rack ends. It had rubbed bared in several spots and was rattling against the plastic of the holder. I scraped off the old black stuff from the holder ends and applied the fuzzy part (not the hooks part) of a sticky backed velcro strip. Whamo. Quiet as a mouse.

Hope that might be your situation as well.

 

I own Prius 2007 for about a month and I notice the same low frequency noise in prius cabin. . I know that one of the reasons is what prius the hatchback, but noise is bother me to much. I am looking for any solutions in a forums as well.