Sound proofing the motor sound?

I rented an i3 on Turo and truly enjoyed 500 miles in this wonderful car. Only complaint was the motor whine became wearing over time, even though it was very quiet.

Has anyone ever sound proofed the i3 to reduce that sound even further?

Personally, I love the sound. For me, it's only noticeable when the accelerator is floored. Sound proofing would just add weight.

I did some experimentation early on in my 2017, using blankets any towels over the cargo floor. I found it didn't make a difference.

There was a distinct difference with the seats up versus folded down to and also with the carpeted floor liner out. I've also driven with the whole motor compartment open and it's unbearably loud.

There's a bit of room for some insulation on the underside of the metal motor bay cover in the BEV. In the REX, it available space seems constrained. It would need to be exterior-rated insulation as the underside of the cover it exposed despite being in a protected space.

I've got to admit that I must have become accustom to the whine — it was never bad with the seats up, just noticable, but I tuned it out after awhile, and my kids never complained, and they have better high frequency hearing than my old ears.

Upon switching from the 2017 to a 2021, I believe it's quieter — not through better insulation, because I saw no difference, so maybe through better bearings in the motor and gearbox?

eNate said:

I did some experimentation early on in my 2017, using blankets any towels over the cargo floor. I found it didn't make a difference.

There was a distinct difference with the seats up versus folded down to and also with the carpeted floor liner out. I've also driven with the whole motor compartment open and it's unbearably loud.

There's a bit of room for some insulation on the underside of the metal motor bay cover in the BEV. In the REX, it available space seems constrained. It would need to be exterior-rated insulation as the underside of the cover it exposed despite being in a protected space.

I've got to admit that I must have become accustom to the whine — it was never bad with the seats up, just noticable, but I tuned it out after awhile, and my kids never complained, and they have better high frequency hearing than my old ears.

Upon switching from the 2017 to a 2021, I believe it's quieter — not through better insulation, because I saw no difference, so maybe through better bearings in the motor and gearbox?

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This is extremely helpful, thank you. I wonder why the rear seats being down would help. The motor is under the rear trunk area, so if the seats were up they would provide more of a firewall between trunk and cabin.

I wonder if the seats down seals a cavity between the base of the seats and the motor compartment?

Having owned a 2014 i3 BEV since new and recently upgraded to a 2021 i3s BEV, there is a difference in tone between the two e-machines (motors).

I find that the 2021's e-machine has a more mechanical-sounding edge than the 2014's. Sound quality is subjective, of course, so I can only say that I like the 2014's sound better than the 2021's, but both are still great to listen to, and preferable to nearly any ICE powertrain (V12s excepted!).

What is a nightmare in the 2021, however, is the synthetic motor noise that is projected outside of the car for pedestrian awareness. It's far too loud inside of the i3 and I wonder if the OP's concern might be related to this pedestrian warning sound? It's truly awful.

I've found some relief in adjusting coding parameters but I haven't found a way to turn the external sound completely, forever and always, off.

That pedestrian acoustic warning system on the 2021 has been such a relief to me after 2 years in the 2017.

While I appreciated living in my silent i3 bubble, the fact is I share this world with many other users, and I got weary of pedestrians (and sometimes cyclists) simply not being aware of my presence. Maybe a hazard of living on a quiet, narrow street and a cyclist-heavy city — I think owners primarily driving in suburbs with wide streets and sidewalks and few pedestrians might be living a completely different experience.

Another suggestion for SuperPoly –

Try a layer or two of Dynamat applied to the e-machine access plate located underneath the cargo area liner. Weight gain shouldn't be significant, I think.

https://www.dynamat.com

frictioncircle said:

What is a nightmare in the 2021, however, is the synthetic motor noise that is projected outside of the car for pedestrian awareness. It's far too loud inside of the i3 and I wonder if the OP's concern might be related to this pedestrian warning sound? It's truly awful.

I've found some relief in adjusting coding parameters but I haven't found a way to turn the external sound completely, forever and always, off.

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The acoustic pedestrian protection system is managed through multiple modules. You need to turn on the iDrive checkbox to control it in the HU_NBT_EVO control unit. Then enable memory of the setting in the VSG01 control unit. There’s a third option to enable/disable the reverse audio signal in the KOMBI_I01_F56 control unit. The current version of BimmerCode handles all three.

Has anyone noticed a NVH improvement (motor noise, or otherwise) with the parcel shelf installed? My car didn't come with one.

Back to the motor noise, most of it seems to originate from the underside of the car, rather than from the rear of the interior. I hear it a lot more as a driver than as a passenger. It's actually fairly inaudible to me as a passenger. Makes sense as the motor is on the driver's side.

I have noticed that some newer EVs use soft sound dampening material on the underside of the car, likely for the high frequencies of the motor. eNate's suggestion seems spot on. I just haven't found a suitable product as of yet.

SuperPoly –

From your most recent post it sounds like you ended up purchasing an i3 – congratulations!

To help us diagnose your noise concern, what year and powertrain is your i3?

frictioncircle said:

SuperPoly –

From your most recent post it sounds like you ended up purchasing an i3 – congratulations!

To help us diagnose your noise concern, what year and powertrain is your i3?

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Thank you! It is a 2017 REx model. I have had it for a few months now.

SuperPoly –

I mentioned Dynamat earlier in the thread, they make an excellent product
https://www.dynamat.com/applications-industries/automotive-and-transportation/

Consider lifting out the trunk liner and covering the cargo floor with one of their roll products. Before you tack it down, drive around with it just resting in place for a bit to see if it solves your problem. Car stereo install shops use Dynamat regularly. If you have one nearby you might even ask them if you could test it out before buying.

With eNate's observation that it's quieter with the rear seats up, perhaps adding Dynamat under the rear seat cushion would help, too.

Sound Silencer https://acousticgeometry.com/products/sound-silencer/ could be a good product to adhere to the underside of the engine access panel. You'd need an adhesive (the Sound Silencer panels do not have any) to glue it to the access panel but Sound Silencer itself is fire-retardant.

I've used this material in my laundry closet to knock down the sound from my laundry machines and it's great, especially with higher frequency noises!

Has anyone noticed a NVH improvement (motor noise, or otherwise) with the parcel shelf installed? My car didn't come with one.

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Can you contact your selling dealer and make them aware that they sold you an incomplete product?

Thank your for your thoughts frictioncircle! I am attempting to find a shop that can apply the sound absorption. I also tried filling the cargo area with soft sound dampening material and other odds and ends to occupy the available space. That seemed to help marginally. Interestingly, the sound is slightly quieter when the rear seats are down. Based on the photos of the CFRP frame I can't understand why that would help.

I purchased the car from a big box retailer where missing items like the cargo cover are considered as-is. I probably could have argued for this at the time though. FWIW, I had the car mechanically inspected prior to purchase.

My inclination is to just sell it because it has gotten to the point where the sound causes pain in my left ear even on relatively short drives. I took it to a trusted independent mechanic and they said everything was normal. I believe this is likely correct, since I rented an i3 for about a week last year and it was similar, but without the pain. I remember at the time being bothered by it only when driving with the windows down, but figured I could get used to it. Music or podcasts don't help enough to make a difference.

Really unfortunate since the car itself is so, much, fun and ticks every other box for me.

SuperPoly –

Dynamat is relatively easy to install, I think some variations are self-stick and others go on with a heat gun and you can cut it with just a razor knife.

If you're considering the Sound Silencer route, you should be able to attach it to the underside of the access panel with a standard construction adhesive.

I also wonder if some of the sound is being conducted through the left side wall of the trunk.

Very sorry to read you may give the car up!