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2010 Toyota Matrix with 72k miles, new grind/rattle sound when engine runs

Starting somewhere in the course of a 400 mile drive yesterday, my car developed a new sound. It sounds like something is either vibrating against something else or some little chunk of plastic is bouncing around in the engine somewhere. At first I thought it was a piece of the bumper or trim dragging on the road, but it’s not. You hear it when the car starts, when the car gets gas, and even when the engine is idling. It’s not a constant sound, but it’s there more often then it is not. It’s there at high and low speeds. It’s there whether the engine is warm or dead cold. To my untrained eye, there’s nothing out of order when I look under the hood. It doesn’t seem to impact performance (yet!).

Since a video is probably worth several thousand of my non-expert words, I’m attaching a link to a video of me taking a drive around the block this morning: https://www.dropbox.com/s/5os26x3ki01rt70/2014-11-17%2008.52.33.mov?dl=0

I’m a first-time poster, but a long time Car Talk fan and have been told by many people to check out this forum. Grateful for any time you take to help me troubleshoot.

I couldn’t hear it in the video.
Where is the sound coming from?
Under the hood? Near a wheel? Heard only in the cabin?

Check your heat shields. It is very common for a bent or loose heat shield to rattle under the circumstances you describe.

A loose or damaged heat shield was also my first guess–until I heard the audio track.
I could be wrong, but it doesn’t sound like any heat shield problem that I ever heard.

As to what the problem is, I can’t tell from afar, but…I can only hope that the OP has checked all of the fluid levels under the hood.

It may be the VVTi gear, this noise most often occurs on cold starts but I have seen cases where the gear failed completely. http://www.toyotapart.com/BRIEF_ENGINE_KNOCK_RATTLE_NOISE_AT_COLD_STARTUP_T-SB-0087-09.pdf I have not heard the link you provided above. As said above heat shields and making sure your oil level is correct should also be checked.

Steve

OP here. Thanks for the suggestions. I just re-viewed the video, and apologize for all the other noises going on. You can hear the problem sound most clearly at about the one-minute mark.

Fluid levels were checked and are all where they should be. I will look into the heat shields possibility. I’ve been looking around for a map or a technical drawing of my car, so I know what I’m looking at when I go down there. (Will have to wait until I get home from work tonight.) The closest I’ve been able to find is something like this: http://parts.bernarditoyota.com/parts/2009/Toyota/Corolla/XRS?siteid=216017&vehicleid=204812&diagram=8428305

If anyone can point me to a better technical drawing of the Matrix’s underbelly, I’d be grateful.

On the heat shield look for cracks around the mounting bolts and welds. Wiggle them to see if they are free from their bolts/welds. Be careful when you do this as they have sharp edges and may be hot if the car has been driven recently.

You might be able to find a helpful diagram on this site:
http://www.toyotapartsoverstock.com/default.aspx