[anakratis]

Originally Posted by GTS Daddy

Is it only on cold start you get the rattle?

You only hear it on cold start for a few seconds and that's it.

Again, BMW would have to re-engineer the rear muffler for the rattle to go away because the AA EL isn't the only culprit. All the non-single midpipes have the same issue...PSI, R44, Akrapovic, Mosselman...

It would seem the solution, hearing from Mike, is to simply pick up a new rear muffler (or axle back). I'm still waiting for my Valvetronic v2 Titanium axle back to see if it fixes the issue.

Rattle is likely caused by increased vibrations in a certain frequency range causing something in the muffler to shake out of spec. A single midpipe simply produces a different vibration that doesn't blow up the rear muffler.

[EatThatLunchBaby]

Good to know that this isn’t just with the AA EL midpipe. I don’t know if this is useful info for anyone looking to purchase, but I 100% think the sound improvement during driving is worth the cold start rattle. It’s just on another level for me when it comes to pushing the car up RPMs. It’s addicting to make this thing scream!

[Drillbit02]

Originally Posted by EatThatLunchBaby

Good to know that this isn’t just with the AA EL midpipe. I don’t know if this is useful info for anyone looking to purchase, but I 100% think the sound improvement during driving is worth the cold start rattle. It’s just on another level for me when it comes to pushing the car up RPMs. It’s addicting to make this thing scream!

100% worth it. And like a post said above, it’s only for a few seconds (maybe 5) of the cold start and then it’s gone. Only on true cold starts when the car hasn’t been driven for 6+ hours.

[GTS Daddy]

Originally Posted by GTS Daddy

I just requested to cancel my AA EL mid pipe order from x-ph. I am not interested in a rattle that gets progressively worse for $2K. Hopefully AA is listening and re-engineers a solution that does not involve changing other components.

Decision retracted. Order is on. We'll see.

[EatThatLunchBaby]

Originally Posted by GTS Daddy

Decision retracted. Order is on. We'll see.

I think you’re making the right choice, the rattle is an inconvenience but definitely worth the trade off IMO. Like Mike said as well, if you really can’t stand it then I guess we will all be getting louder with axel backs 😁

[CaptBoaty]

The improved sound of the AA EL easily outweighs having to hear the rattle during the 30 seconds of cold start.
But I really am curious on what exactly is causing it.

[mike@x-ph.com]

Originally Posted by CaptBoaty

The improved sound of the AA EL easily outweighs having to hear the rattle during the 30 seconds of cold start.
But I really am curious on what exactly is causing it.

Do we know if disabling the cold start eliminates the issue?

[anakratis]

Originally Posted by mike@x-ph.com

Do we know if disabling the cold start eliminates the issue?

It should. The rattle only happens on cold start. You don't hear it when driving around at 1-3k RPM.

[static_void]

Originally Posted by mike@x-ph.com

Do we know if disabling the cold start eliminates the issue?

I'm theory it should. No rattling from my car when it's started up while warm. It's only on cold start.

[agnewfedaykin]

Installed mine two weeks ago an I have the same rattle. I did have trouble fitting mine on the passenger side down pipe. I had to shave down a lip on the inside of the mid pipe it was hitting and grind down the edge of the cat pipe that sticks out past the flange to get it to seat properly.

Maybe the tolerances aren’t close enlugh or to close and the tubing is hitting the inside of the midpipe until heat expansion kicks in? I was thinking of using an oscillating saw an cutting the tube down a quarter inch might fix it.

[HiFi]

are you guys sure the rattle is in the rear muffler - F80 used to suffer a lot from wastegate rattle on cold start

[CaptBoaty]

Originally Posted by HiFi

are you guys sure the rattle is in the rear muffler - F80 used to suffer a lot from wastegate rattle on cold start

It’s definitely from the rear of the car.
It most likely is resonance induced from the x-pipe design. From what I understand, our rattle is almost the same as what people were experiencing from the PSI mid pipe…which is an x-pipe.

[EatThatLunchBaby]

Originally Posted by HiFi

are you guys sure the rattle is in the rear muffler - F80 used to suffer a lot from wastegate rattle on cold start

I’m not going to pretend I know what is causing it at all but it definitely sounds like it’s really far back in the exhaust system

[anakratis]

A little sound clip for ya'll

https://www.youtube.com/shorts/OXxzKIfW3aY

[Boogie2121]

2k on a midpipe and y’all are saying a rattle is okay lol. I would make AA answer for it, half the folks on here are the people who put the pitchforks on Valvetronic bc they make their exhausts in China. I rather have a reliable exhaust made in China than one that rattles like a 94 civic on startup. I would push for an answer…

[anakratis]

Originally Posted by Boogie2121

2k on a midpipe and y’all are saying a rattle is okay lol. I would make AA answer for it, half the folks on here are the people who put the pitchforks on Valvetronic bc they make their exhausts in China. I rather have a reliable exhaust made in China than one that rattles like a 94 civic on startup. I would push for an answer…

Again, it isn't really an AA problem. Any X-pipe configuration with stock rear box has this issue on cold start.

[SevenNine]

Originally Posted by anakratis

Again, it isn't really an AA problem. Any X-pipe configuration with stock rear box has this issue on cold start.

Does Dinan and AWE have the same problem? I think it's only AA and PSI.

[anakratis]

Originally Posted by SevenNine

Does Dinan and AWE have the same problem? I think it's only AA and PSI.

The Dinan topic does mention the rattle a couple times, though they have attributed it to the exhaust valve. I don't believe many people have ordered the AWE midpipe only, at least not from what I've seen. Changing the rear box alleviates the issue AFAIK.

[EatThatLunchBaby]

It’s so odd to me that it would be just the resonance from the X-pipe design. I’m not saying it’s wrong but it distinctly sounds like it starts normal (~1 second), then mechanical rattle from the rear (~5 seconds), then loud resonance sound (~ 20 seconds) until the RPMs drop to normal idle levels

[M4Lou]

My ER has a bit of a rattle on cold start. Goes away when RPM kicks down. This is the stainless/standard length - h-pipe set up.I'

(I've got a stock axle back and stock valves)

[CaptBoaty]

Originally Posted by SevenNine

Does Dinan and AWE have the same problem? I think it's only AA and PSI.

Can’t really compare Dinan and AWE as they retain the secondary cats.

I knew this could have been a problem when I initially ordered the EL pipe. There is always a risk when someone is among the first to get a new product.

I had almost the same issue on my mustang when I installed Long tube headers with an X-pipe. Although that car did not have valves in the exhaust, the resonance matched the natural harmonics of the exhaust hangers and crated a slight rattle. Luckily that car was so loud at startup that you really could not hear it.

X-pipes create resonance, almost like a pressure differential from when the exhaust collects again on the exit. It just so happens that the resonance is close to a natural harmonic of something located in the stock exhaust can. What the actual rattle is…I have no idea.
I’m not an engineer but adding length to the x pipe could be a potential fix (alter the resonance freq).

I don’t blame AA, PSI, or any other X-pipe manufacture as they most likely engineer and test their products as a package, i.e with their axle back connected.

[mike@x-ph.com]

This issue has more to do with removing the cats than the brand of the downpipe.

Option 1 - get a resonated or catted midpipe, no cold start rattle but also a milder volume increase

Option 2 - Get a non-catted and non-resonated midpipe, cold start rattle for a few seconds, then enjoy the sound for the rest of the time.

Option 3 - upgrade your axle back and get the best of both worlds