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2018 Silverado here. Over the winter I noticed a prominent rattling coming from somewhere underneath the vehicle that was made worse whenever I am stopped but in drive. For example, its the absolute loudest/worst when I'm going through a drive-thru and having to move forward and stop, move forward and stop, etc.

Finally I noticed I could hear it rattle momentarily even when the truck is completely off and someone slams one of the doors hard.

I went under the vehicle this morning and poked/prodded around and seemed to have found the spot where the rattling noise is coming from. Its either the muffler or a part of the exhaust:

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I uploaded this YouTube video which shows the rattling happen when I bang on this part with my fist.

Anybody have any idea(s) as to what could be making this noise, and what the fix is?

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  • A problem with an exhaust hanger, missing donut etc... most likely. SOMEBODY has to crawl down there and look. Clearly, that's not you, since you haven't done it. So take it to someone.
    – Harper - Reinstate Monica
    May 1, 2022 at 10:13

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It just sounds to me like the inside of the muffler has deteriorated and is now rattling. About the only "fix" for it is to replace it.

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  • Thanks @Paulster (+1) -- If thats the case, I'm guessing there's not anything "wrong" per se and that its just more of a noise nuisance more than anything, right?
    – hotmeatballsoup
    Apr 30, 2022 at 16:53
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    @hotmeatballsoup - Well, that depends on how you look at it. The "rattling" piece inside of the muffler can cause blockage in the exhaust flow. This can hurt gas mileage. I have a 2018 Silvy ... I know what kind of mileage it gets, LOL! It is not an emergency, that's for sure. Just something you'll want to get replaced as you get time/funds. At least I'd want it replaced.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Apr 30, 2022 at 19:09
  • @hotmeatballsoup could well be an easy and minor fix, right now, but untreated it could destroy your exhaust system.
    – Harper - Reinstate Monica
    May 1, 2022 at 10:19
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Possibilities in order of likelihood:

  1. The heat shield on top of the muffler. Check and secure as necessary.

  2. One of the catalytic converters is breaking apart, and chucks of the ceramic blew into the muffler. You'll tend to get a MIL (check engine light) with a converter loss-of-efficiency code.

  3. Internal baffle inside muffler.

Any of these need to be repaired. So if the heat shield is good pull the muffler. And if you don't hear pieces sliding around inside (sometimes you can shake them out) then replace the muffler.

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