Rattle/Noise on Cold Start

[tdstuart]

2015 Mustang Gt Automatic ~96k miles
Only mods are an MBRP Exhaust (street version with H pipe).

EDIT: Exhaust seems really solid. Having hard time pinpointing the noise. Only happens on cold starts for like 5 seconds. Even after one start and shutoff it will take several hours for the car to cool enough for it to happen again. Probably going to pay the dealership to check it out.

Uploaded the audio clips to YouTube but during mostly cold starts my car will make a clunky and metallic sound. It goes away after a few seconds but I swear it started a week or two ago and has just been getting worse. I’ve had the exhaust for probably like 3 months or so.

I swear it’s the exhaust and I’ll probably check on the clamps and see if anything is loose or something but it worries me that it only happens during cold starts and not even revving.

If anyone has had a similar problem or can give ideas any feedback would be greatly appreciated.

Cold Start with Rattle Video (Rattle starts about 0.5 seconds after car fires up and quickly dies down:
https://youtube.com/shorts/fznyb60vWvc?feature=share

Normal start (no rattle):
https://youtube.com/shorts/9350ZWZumVU?feature=share


Light Slow Revving (no rattle):
https://youtube.com/shorts/0IVwY9SRvhA?feature=share

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[tdstuart]

Started the process of finding source of the rattle. All the exhaust clamps seemed good. Having a hard time pinning down exactly where it is coming from. Gonna wait for it to cool down get underneath the car and see if I can find it.

 

[slime_bullet]

Started the process of finding source of the rattle. All the exhaust clamps seemed good. Having a hard time pinning down exactly where it is coming from. Gonna wait for it to cool down get underneath the car and see if I can find it.

Try tapping on the trans inspection plate

 

[tdstuart]

Try tapping on the trans inspection plate

New to cars but I think I figured out what that is lmao. Started up the car this morning and the noise was too loud to pinpoint when I was under it.

I tapped on what I think is the trans inspection plate (after the startup). It does make a noise similar to the one on startup. Going to wait for the car to cool down a bit more and check again. Could make sense given It was pretty hot so the metal could have expanded stopping the noise.

If it is the tans inspection plate what would be the fix? I only looked for a second and only could see one bolt that looked like it was holding the plate on. It was at least hand-tight.

 

[slime_bullet]

New to cars but I think I figured out what that is lmao. Started up the car this morning and the noise was too loud to pinpoint when I was under it.

I tapped on what I think is the trans inspection plate (after the startup). It does make a noise similar to the one on startup. Going to wait for the car to cool down a bit more and check again. Could make sense given It was pretty hot so the metal could have expanded stopping the noise.

If it is the tans inspection plate what would be the fix? I only looked for a second and only could see one bolt that looked like it was holding the plate on. It was at least hand-tight.

I got some high temp gasket maker and made a gasket between the plate and trans

 

[tdstuart]

I got some high temp gasket maker and made a gasket between the plate and trans

How did you figure out this was the issue?

And maybe ill try sticking a piece of paper or something in between the plate on the next startup so I can see if this is the issue.

 

[tdstuart]

I got some high temp gasket maker and made a gasket between the plate and trans

Tried sticking some paper in between the gaps so it didn't make a noise anymore. Started the car and I'm pretty sure I still heard it. The sound goes away really fast when it isn't cold.

I leave it for another hour or so and see if I can tell then.

 

[slime_bullet]

Tried sticking some paper in between the gaps so it didn't make a noise anymore. Started the car and I'm pretty sure I still heard it. The sound goes away really fast when it isn't cold.

I leave it for another hour or so and see if I can tell then.

Come on man paper??? You're going to catch your car on fire! That gets hot as shit! Stick some washers or some quarters instead.

 

[tdstuart]

Come on man paper??? You're going to catch your car on fire! That gets hot as shit! Stick some washers or some quarters instead.

Rattle only happens during like first 5 seconds of startup and I shut it off after it stops. Paper isn't meant to be a temporary thing just something that would dampen the noise on the startups. Im sure it would catch on fire if I let it stay on for a bit.

Anyway, I started it again and the rattle is just as clear and present so it's not the trans inspection plate.

 

[tdstuart]

Update: Took it to the dealership today. Had to pay $155 for diagnostics smh. They are backed up so should be atleast a week till they are able to look at my car. Hopefully I’ll get some feedback. Dealership guy said it sounds like the exhaust… hopefully they will find a fix.

 

[tdstuart]

Update: Got the car back today. Turns out it was the exhaust. One of the clamps got a little loose and allowed the exhaust to move around. Created a small leak and just enough weird vibration to cause the noise. It must have been a pretty small gap because it would only take a few seconds for the exhaust to heat up enough to expand and stop the leak.

So note to anyone experiencing the same issue. Go through your entire exhaust even if everything seems good and check fitment and clamp tightness before you freak out and take it to the dealership.

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