420D Muffler delete causing VERY LOUD whistle?

[RyanMCR_F32]

First of all, I'm looking for help not sarcasm and people telling me what I should have bought instead etc. If you can't help or be friendly then don't bother... I've asked this question on a lot of places and keep getting sarcasm about my choice of car or "deletes muffer moans about sounds" comments...

Recently took my 2014 BMW 420D for an exhaust tip conversion, only the last rear muffler deleted and converted into twin pipes (one on either side to match the new rear diffuser, I wasnt particularly bothered about a muffler delete but it was needed so it matched the new rear bumper/diffuser) Now I'm getting a VERY loud whistle which only happens at 3K rpm onwards...

EVERY other 420D / 320D with this work done sounds great, not much difference in sound at all. So why is mine making this incredibly loud noise.

I've noticed that if I do a hard pull in 2nd or 3rd it seems louder (assuming this due to more pressure)

I know people may mention the turbo however it's never made that sound before, the car is only on 26K miles and has been looked after. NO symptoms of a bad turbo so far.... power is good, sounds healthy usually, no leaking sounds from the engine bay, It only occurred after the exhaust work.

My first assumption was either a tiny leak which is only making a noise when a significant amount of pressure builds up (like an old kettle) OR the shape of the pipes/tips is causing a very unusual flow of air and causing a howling which then turns into a high pitch whistle.

Here is the example, the loud noise is right at the end of the video - https://www.youtube.com/watch?v=FV0a3k5d-cs

I will be returning to the garage for them to inspect and if we cant figure it out, we will have to remove and see if it still makes the sound. Im 99% sure this is something to do with the actual exhaust fabrication and not just "turbo whistle" half the people on here clearly have read the title and not bothered watching the entire video...

Edited by RyanMCR_F32 on Wednesday 3rd February 23:12

[normalbloke]

Does it still do it when you put the muffler back on?

[RyanMCR_F32]

I haven't re fitted the old muffler yet, all I can say is that the car was fine on the drive down there, we cut it off and they fabricated a twin pipe for me and now it makes this sound.

[Mastodon2]

Sounds like a just reward for cutting silencers out from a diesel exhaust.

[Mo28]

Someone local to me had a C220d made into a C63 rep and their car would make a similar whistling noise as well. There's was converted from a single exit to a quad exit.

[RyanMCR_F32]

Thanks for reading the opening line of this post, very helpful. Heard MULTIPLE cars with this engine and their muffler deletes sound great. Apart from that noise, everything else sounds miles better, sportier, lower rumble at low rpm. More turbo noise. All good expect that noise.

[Turn7]

Opens Popcorn.....

[RyanMCR_F32]

Mo28 said:

Someone local to me had a C220d made into a C63 rep and their car would make a similar whistling noise as well. There's was converted from a single exit to a quad exit.

Did they find a fix or a reason? Like I say, my guy who took me to this fabricator has taken 100 cars and never had an issue, including a few N47 engines. He is baffled.

[marksx]

This appear the first time you drove it with the new exhaust?

This is going to sound patronising, it's not meant to be - turbos are loud! The design of the exhaust may just be that now it's amplifying a certain frequency.

[Mo28]

RyanMCR_F32 said:

Did they find a fix or a reason? Like I say, my guy who took me to this fabricator has taken 100 cars and never had an issue, including a few N47 engines. He is baffled.

Wouldn't know, never spoke to them. Just remember being disappointed every time I saw that thing driving past and not hearing a V8 rumble.

Might be worthwhile getting an opinion from another exhaust fabricator.

[normalbloke]

RyanMCR_F32 said:

Mo28 said:

Someone local to me had a C220d made into a C63 rep and their car would make a similar whistling noise as well. There's was converted from a single exit to a quad exit.

Did they find a fix or a reason? Like I say, my guy who took me to this fabricator has taken 100 cars and never had an issue, including a few N47 engines. He is baffled.

Have you tried deleting the turbo? Process of elimination and all that...

[Alex_225]

As already said, it'll be the turbo sound. They can make a fair bit of noise even without the likes of a blow off valve. If you open up the sound from the exhaust or the induction, you're going to open up the sound of the turbo. If you've removed one of the silencers that sound is the result.

I'm not sure if you're concerned that something is broken so don't worry on that part but it's likely that's exactly what would happen.

[RyanMCR_F32]

marksx said:

This appear the first time you drove it with the new exhaust?

This is going to sound patronising, it's not meant to be - turbos are loud! The design of the exhaust may just be that now it's amplifying a certain frequency.

Yes, like I say it only appeared on the first test drive out and they've done this exact same thing to other 420D/320Ds and no issues. Youtube is also full of muffler deletes on this car and they sound fine.

[Benbay001]

It could be something simple and unimportant like the sound of disappointment.

[drdino]

Is it coming from the rear or from the engine bay?

[ZX10R NIN]

Mastodon2 said:

Sounds like a just reward for cutting silencers out from a diesel exhaust.

The DPF etc are still there it sounds like he's removed the resonator box, so maybe chill out a bit.

[marksx]

dibbers006 said:

I did the wife delete about eight years ago and nearly all annoying noises stopped.

this amused me

[MrGTI6]

RyanMCR_F32 said:

He is baffled.

[Scrump]

RyanMCR_F32 said:

First of all, I'm looking for help not sarcasm and people telling me what I should have bought instead etc. If you can't help or be friendly then don't bother... I've asked this question on a lot of places and keep getting sarcasm about my choice of car or "deletes muffer moans about sounds" comments...

Recently took my 2014 BMW 420D for an exhaust conversion, muffler deleted and converted into twin pipes (one on either side to match the new rear diffuser, I wasnt particularly bothered about a muffler delete but it was needed so it matched the new rear bumper/diffuser) Now I'm getting a VERY loud whistle which only happens at 3K rpm onwards...

I've noticed that if I do a hard pull in 2nd or 3rd it seems louder (assuming this due to more pressure)

I know people may mention the turbo however it's never made that sound before, the car is only on 26K miles and has been looked after. NO symptoms of a bad turbo so far.... power is good, sounds healthy usually, no leaking sounds from the engine bay, It only occurred after the exhaust work.

My first assumption was either a tiny leak which is only making a noise when a significant amount of pressure builds up (like an old kettle) OR the shape of the pipes/tips is causing a very unusual flow of air and causing a howling which then turns into a high pitch whistle.

Here is the example, please watch it ALL as the noise is towards the end- https://www.youtube.com/watch?v=FV0a3k5d-cs

Any advice is welcome! Thanks

I have no experience of muffler deletes on a diesel, but welcome to PH.

[Roboticarm]

Wondering if the exhaust mod has affected the back pressure ?
I'd be tempted to revert to the original exhaust and see if the noise goes away.

Years ago I had a custom exhaust on a rover 220 turbo and the design meant I gained back pressure, had to revert back to get the performance back.

Mine looked lovely and the welding as excellent but it wasn't doing the job

https://dieselnet.com/tech/diesel_exh_pres.php

Edited by Roboticarm on Monday 1st February 20:13