Rattle after Cat protector installation

hard to believe they can't figure a way to move/bend it so it doesn't touch. maybe a local mech or muffler shop could help, or at least show you the problem area.

if they will remove it, try another brand?

 

Which protector?

 

I'll assume you're referring to the Cap City Muffler security plate or a similar knock-off brand.

Have a muffler shop replace the two rubber hangers that hold the muffler/resonator close to the under chassis. If they are worn, then they hang too low and allow the catalytic converter to vibrate against the plate.

Rubber Exhaust Hangers

 

Is it the big plate over the whole area or the type with all the metal cable?

 

I used Miller Cat shield on 2007 gen 2 Prius. I had a rattle at low speeds also. I had the luxury of personally putting on a rack and inspecting it myself. I spotted issue quick. I have to give credit to The Lizard King above. New Rubber exhaust hangers will fix the issue. For sure! Method #2 is look at cat shield through VENT and look for scratches on cat. Let’s say you see 2 scratches where cat shield VENT rubs on catalytic converters. Use pliers and bend the vent back and forth. Like an open lever on top of soda can. VENT on cat shield snaps off in two bends. Easy!

 

EmilyF

EmilyF in regards to your story. If your car is a Gen 2 Prius, the shop is right

EmilyF I’ve been thinking about your story. It’s a little off but I figured it out. When you mentioned shop. Is it where you got new catalytic converter installed or shop where you got cat shield installed?

Anyways it doesn't matter because I have the answer. After your catalytic converters was stolen, a new cat was welded on by a muffler shop. After the repair maybe the exhaust system hangs lower. Like exhaust system has different bend. Which is all good. Then you went to auto repair shop to install cat shield.

EmilyF the shop is right. Your cat protector is rattling on exhaust system. After cat being stolen, a muffler shop welded new Catalytic Converter on. When the cat repair was done, it has a different bend or hangs lower. Which is a great repair!

Then you installed a Cat protector. I’m just making up the story but who knows. Either way the fix is simple, you need space between Protector and Cat. Using the lizard king or my method should work.

If that doesn’t work, bring it to a muffler shop. Tell them about the Cat protector rattling. They will re-bend the exhaust system pipes to get clearance needed. No more rattle. Problem solved!

 

It sounds as if the shop didn't install the shield " correctly". I put a Cap City Muffler shield on my 07- in the instructions for this unit they tell you to temporarily place a 2x4 between the shield and exhaust while installing to provide clearance and prevent the shield from vibrating (oil-canning) afterwards.

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Does anyone know if the above solution will work for the (millercat) stainless steel shield? I would assume it would be harder to bend versus the aluminum version

 

Yes, sheet stainless steel will bend just like aluminum.

 

I installed the CCM "Cat Security" shield on my Gen 3 and have had a rattle ever since. Like others, the rattle occurs during acceleration, but usually only when the ICE needs to turn on (i.e. on a hill or when harder acceleration is needed). The rattle would go away when I ease off the accelerator and/or when I get up to speed. It is especially annoying in stop and go situations, such as stop signs and traffic lights.

I got under the car and tapped around where the sheet metal meets the frame, but found that the shield was pretty close to the cat as well.

After a bit of searching, I came upon this thread that recommended using the rubber exhaust hangers that CCM conveniently sells. When I received it, it was obvious the hole-to-hole distance was shorter on the new hangers and should theoretically lift the cat away from the sheet metal.

Unfortunately, this seems to have made the rattle more noticeable somehow. I'm now questioning whether the rattle is coming from somewhere else. I did notice, however, that the new hangers are a bit softer than the stock hangers (which were still in great shape after ~105k miles). In the meantime, I've ordered some hard polyurethane hangers with the same hole-to-hole distance as the short hangers supplied by CCM.

 

This method of bends in the plate for clearance worked for me.

 

The shop most likely did it right. On your install it could have went either way. After removing the 2x4, it would have been possible for the catalytic converter to vibrate on the metal shield. In your case, it worked out.

 

On a Gen 2 catshield plate three shallow radial bends over a 2x4 before installation is the guaranteed method to avoid "oil canning" or any contact at the rear with the catalytic converter. A downward bend at the middle and two upward bends from the same vertex at the front center of the plate spreading out at the trailing edge would solve any vibration and eliminate any contact with the catalytic converter.

 

I just had one installed. It was the first one the shop had ever put on. It rattles at slow speeds like others here. Has anyone found a way to fix this if the plate is not bent before installation? Did any rubber hangers end up working? Can you bend it after installation?

 

Out of curiosity, are any of the replacement cats mentioned here OEM or are they aftermarket? The original owner of my gen 2 had hers stolen and replaced at a Toyota dealership with an OEM unit and a shield. Plenty of clearance and no rattles.

 

I'm having the same problem with my 2007 Prius, owned since new, after my Toyota dealer installed the MillerCAT stainless steel shield, after having replaced the stolen catalytic coverter with an OEM one. I also had them replace the entire exhaust system, as well as all the hangers, all OEM. The rattling noise tends to come at low speeds, and oddly, seems worse when it's cold (freezing temps or below). Does anyone know of a fix? The MillerCAT website suggests that another potential cause of rattling could be a bad engine mount. I'll go back to the dealer soon for regular maintenance and will ask them to check the engine mounts.

 

Maybe something in the new exhaust system is rattling and not the shield

 

We had the MillerCat stainless steel installed by our regular mechanic. He spent two extra days unsuccessfully adjusting things trying to stop the rattle at slow speeds. New hangers didn't help. There apparently is just not enough room to do much about it. He did offer to make some more adjustments for free if someone does come up with a good solution to the problem. For now we're just living with it.

 

I wonder why the shield people all make flat panel shields instead of shields that have a more three dimensional shape that affords a small bit more clearance. I realize it’s cheaper to just cut a sheet of metal than use a press to shape it but the press is not that expensive to use. Getting access to one may be difficult for a small shop. Maybe that would avoid the rattling problem?