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Discussion Starter · #1 ·
My 2020 has about 22k miles on it. I started noticing a brief rattle that occurs within the first 20 seconds of a cold start. Any ideas?

Below is a video:
 

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My 2020 has about 22k miles on it. I started noticing a brief rattle that occurs within the first 20 seconds of a cold start. Any ideas?
Possibly 2 different areas maybe more...
1. Lifters
2. Fuel Injectors

Perhaps Hodna can listen and see if it sounds like his crankshaft or rod bearings?
 
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Discussion Starter · #3 ·
Thanks @DJVAN. I have an appointment with the local dealer next week. I will report back on what they find.

First thought that came to mind is the timing belt tensioner but it seemed too brief to be it.
 
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We also have a 2020 Odyssey EX, just under 16,000 miles since purchased new in April 2020 (Jacksonville FL area), and the sound I heard on the video (while not a "rattle" as I think of them, though my hearing is not what it used to be!) seems the same as on ours when the A/C compressor engages shortly after cold start, then only a few seconds later disengages. Ours does that A LOT, like every minute or less, then gradually becomes less frequent and longer between A/C engage and disengage after it warms up and the inside air temperature cools down. I can also feel it through the driver's seat. That amount of frequent cycling concerns me since I worry some that it could lead to premature compressor failure, but I have yet to discuss it with a Honda shop since it could probably only be duplicated after they kept it overnight and I don't want to be without our primary vehicle just to have them tell me (pessimist that I am) they could not duplicate it and or that it is "normal".
 

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I couldn't hear anything bothersome in the video.

I used to have an aluminum block Camaro which would rattle like a diesel until the motor got hot. The fancy pistons in the iron sleeve block were designed to have the bare minimum hot clearance, so cold there's a lot of slop. People with iron blocks and forged pistons often report similar.

If it's the A/C cycling, might check what the low side pressure is doing meanwhile. From resting, you can pump out all the refrigerant from whatever low side "reservoir" there may be, before the returning refrigerant from the loop comes around to start making it up, if refrigerant charge is low. Getting all the way back around through the evap and condenser takes a while. Once it's "up on plane" you might well see a lower (but still) cycling rate.
 

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Discussion Starter · #7 ·
seems the same as on ours when the A/C compressor engages shortly after cold start, then only a few seconds later disengages.
Thanks JKD, I don’t remember if I had the A/C on when I took the video. I did put the car in On mode for 30 seconds before starting the engine.

On mine, I only started noticing it this week, after a 2,500 trip. I will keep an eye on how the A/C compressor engages and disengages as you mentioned.
 

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Discussion Starter · #8 ·
I couldn't hear anything bothersome in the video.
Sorry, it could have been captured better. It is the clanging noise that starts at about 10 seconds in and goes away at about the 19 second mark. Almost sounds like something is loose and is vibrating against something. But it only happens at cold start.
 

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Do you notice excessive engine shake at cold start?
Maybe motor mounts / dampers are letting the engine
roll and banging exhaust against something. Whether
it's a cold start transition problem, or a rubber problem,
I guess is another experiment for the list. But if you
had it overhead you might be able to see a shiny spot
where metal hit metal, could maybe grief on the
exhaust plumbing to see if it's got potential to touch
something (or signs of so doing), etc.

Might get someone to do the starting while you peer
into the engine bay and concentrate. Video is no
substitute for eyes and ears up in it.

Does it start and cease abruptly, or does it fade in
and fade out more slowly? Become intermittent
or change more simply in volume?

Are there any loose tubes, hoses, cables, trim
that happen to make the right note when you tap
them (going by the "clanging") with a screwdriver?
 

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DJVAN, it doesn't resemble the knocking or rattling I hear on my 2018, which is always there. To me, that sounds like an exhaust or heat shield part that needs to expand just enough from a bit of warm exhaust to stop the rattle. Definitely ask the dealer.
 

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Discussion Starter · #12 ·
Thanks @Hodna. I’m not too worried as long as it’s not something major like the timing belt tensioner. I have an appointment with the dealer on Monday. Since it only happens at cold start, I know I have to leave it with them. Hopefully, they can figure out what it is.
 

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At the time of my 2014 with 36,000 miles on it had a cold start rattling/ gurgling / growling noise to it and would only happen on first start winter or summer. All other starts for that day you would not hear it. After much online searching for possible culprits and the location of the noise- (around the power steering pump) I had 2 possibilities;
1. power steering pump had a hose fitting issue causing it to get air into the system and causing a low growling noise and after running it for a while air would work itself out.
2. timing belt tensioner.
Fast forward to 3 years later and now my Ody has 100,000 mikes on it and now growling / rattling noise is constant all day long but not really louder than at 36,000 mikes. I have dealer ship change out timing belt and tensioner because it’s that time and the growling / rattling noise goes away and have not heard it for last 2 years.
More than likely belt tensioner if your noise is around the power steering pump area.
 

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Doesn't hurt to use a mechanic's stethoscope or similar to try and isolate the noise.
 
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