Odd single metallic “knock” occasionally on startup

[GTP]

Mine does it too.
Not sure I had it before.
Strange.

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[Bman5150]

@GTP snd @thunderstrike - do you guys have active exhaust?

 

[sk47]

Hello; Same sort of thing has happened on other types of cars due to some part of the exhaust banging into something. An engine will rock on the engine mounts sometimes harder than other times for some reason. I have a guess or two but will keep that to myself. Anyway, I have traced the noise to the exhaust.

 

[GTP]

@GTP snd @thunderstrike - do you guys have active exhaust?

I do.

 

[PoCoBob]

@GTP snd @thunderstrike - do you guys have active exhaust?

I do not.

 

[geep81]

No, and I still occasionally have the noise on startup. It sounds like piston knock for a second but I think it could also be the active exhaust closing from its last position, which is often. Sport or track mode.

Turn on quiet mode on your exhaust settings, set it to be quiet at the time it currently is, start the car and put it in track mode and then shut it off.

Then, with your driver door open, turn the car back on to ignition 1 mode/do not start it. Do you hear the same noise? If your exhaust is in quiet mode, and you shut off in track, it will close the flaps when you first turn on the car. Door open lets you hear it better.

It makes a metallic noise. Maybe that's your sound?

 

[Bman5150]

@geep81 I’ll try that. Thx.

 

[machncheese1]

Mine does it too.
Not sure I had it before.
Strange.

Did you figure out the concern? Mine is also doing it too. Don’t remember if it did it before or not.

 

[machncheese1]

Have you ever figured out what was causing the noise? My 2019 GT is also making the same noise.

Any updates??? I been having a mach 1 for 5 months now

 

[machncheese1]

I’ve got a brand new Mustang GT with active exhaust and the 10-speed auto. It’s only got about 390 miles on it so far, and I’ve had it for just three weeks. I’ve noticed an odd startup sound every once in a while. The car seems to slightly stumble on startup and I hear a singe metallic knock sound-it sounds like engine knock but it’s just one single knock noise. Car runs perfectly fine in all respects.

Anyone ever hear this in their Coyote V8? It definitely doesn’t sound normal to me, but I’ll bet it only happens about 1 out of 10-15 starts. Also seems like it’s only happened after I’ve driven it for a period and the engine is warmed up to operating temperature (but not always.)

Did you ever figure out what it was??? Any further issues ??

 

[GTP]

No. Active exhaust flap seems like the best theory.

 

[Bman5150]

The procedure outlined in @geep81 ’s post did not produce the sound. It’s a rare occurrence and sounds like a rattling piston for like two knocks. Almost like the motor isn’t igniting immediately but once it does all is fine. Zero issues with the car and no abnormal oil usage. In fact, the car used no noticeable amount of oil in between a very long interval oil change (1 year/4500 miles.).

 

[sk47]

It’s a rare occurrence and sounds like a rattling piston for like two knocks. Almost like the motor isn’t igniting immediately but once it does all is fine.

Hello; New theory. I discovered something with my four-cylinder car years ago. I sometimes would start it up to pull it into the garage a few feet after it had sat long enough for the engine to get cold. I would shut the engine down within moments and for sure before it had warmed up.

The next time I would start it the engine would run rough for short time then clear up. Much as you describe. My theory is during the very brief running time the fuel mix is a bit rich. That the next day some small bit of that fuel is still in the cylinder(s) which stopped with the valves closed.

Anyway, i try to not do that sort of thing anymore. I now will let the engine run for a bit longer thinking it will get out of a "rich" startup mode. Anyway, such seems to make a difference.

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