[Gutgenug]

I have a Fortwo Cabrio Passion, 2008. It has been in storage for three years but I got it back about a year ago.
I had it checked out twice by dealerships and it was given a clean bill of health.
However, lately there has been a really strange noise. When turning it over there was what I can only describe as a deep base sound, almost like a reverberation in a speaker. It happened randomly and when I could not make it happen (it continued but randomly, seemed to be no set pattern to it) I decided it would not be worth taking it to a shop. Figured it would not happen when I was at the shop and they would think I was nuts.
Then, today, on the way home the noise came back. This time while I was driving. The radio is never used, I listen to audio books on my blu tooth ear plugs, but this was really loud. It scared me so I pulled over. It stopped. I turned the car off, back on and got back on the road. It came back but then went away. I was only about 3 miles from home so I went on home and parked the car. I turned it off and left it for a bit. Turned it back on and I get the loud thump when I turn the key and the ignition starts, but it goes away.
The car seems to run fine, no vibrations, no other issues. The brakes were recently done (after sitting for three years they needed a complete change out), back tires replaced and some other maintenance but nothing I can connect to this.

Any ideas? I am open to all suggestions.

 

[Jo e Lefors]

Yes PM sent

 

[Gutgenug]

Thanks to Jo e Lafors!!! It was the subwoofer. One plug pulled out and the Strange Scary Noise is gone!!

Now I will sleep well tonight

THANK YOU

 

[duckhunter9090]

Been there, done that. Took me awhile to isolate it. Mine is unplugged.

 

[dsoukup]

So what is the cause of this "farting" noise coming from the sub woofer? I have replaced the capacitors in the sub to no avail. I noticed I can make it "fart" by pressing on the up or down window buttons when the windows are already all the way up or down. I can also make it happen if I step on the brake pedal at a stop sign... really any time I put a load on the electrical system at idle. I'm beginning to think it might be a low voltage situation. Perhaps the voltage at the sub amp is low due to a bad positive or ground? Does anyone know the pin outs at the connector to the sub? I have a feeling a lot of people have encountered this situation.

 

[MB DNA]

	... really any time I put a load on the electrical system at idle. I'm beginning to think it might be a low voltage situation. Perhaps the voltage at the sub amp is low due to a bad positive or ground? What MY smart, age of your 12V?

 

[Jo e Lefors]

Couple of years ago I unplugged my subwoofer because of the noise is it was making. I'm going to check out the low voltage theory. The beginning of this year I purchased a new battery Duracell absorbent glass mat battery from Sam's Club. Today I plugged my subwoofer back in and we'll see if it starts making the weird noises. If it doesn't make weird noises then I think we have found a low voltage warning signal for a battery that's going bad.

 

[MB DNA]

I was shocked to find that a battery (AGM) change may have fixed my growling sub!

A couple weeks later, all is good…

MY09 451, under seat subwoofer droning

Garage Queen 09 Brabus with 15,700 miles had become “possessed” emitting random droning noises from the subwoofer. Upon starting, turning off, radio on & off. Had plans to replace the subwoofer but ironically thought that I’d change the 2012 (9 year old) 12V (flooded) battery first. Swapped...

www.smartcarofamerica.com

 

[Jo e Lefors]

I was shocked to find that a battery (AGM) change may have fixed my growling sub!

A couple weeks later, all is good…

MY09 451, under seat subwoofer droning

Garage Queen 09 Brabus with 15,700 miles had become “possessed” emitting random droning noises from the subwoofer. Upon starting, turning off, radio on & off. Had plans to replace the subwoofer but ironically thought that I’d change the 2012 (9 year old) 12V (flooded) battery first. Swapped...

www.smartcarofamerica.com

Sadly not here. As I stated in above post I got a new battery at the beginning of the year and just yesterday plug my subwoofer back in. Last night while taking Evelyn up to the park, when I turned off the car the burping or farting sound happened then again at home.
Today same thing turn the car off at the park and It made the sound, turn the car off in the garage same thing. I went ahead and unplugged it again.

 

[wahi]

The mystery remains...

 

[Favwoir2021]

Yes PM sent

Hi Where is the sub woofer located please and what cable? this noise has ;asted for the past 1.5hr drive normally its quiet or short time. Thanks

 

[wahi]

Under driver's seat. Cable comes out from a slit in the carpet there, a bit to the right. REmember to disconnect battery if you're taking off the seat for better access.

 

[Jo e Lefors]

From Las Vegas NV
Welcome to SCoA forums
You Do Not have to remove any seats to unplug the subwoofer on a U.S. spec 451.
U.K. smarts may be different.
Take a look at the picture in Post #18 at this link

What computers are under drivers seat? FLOOD CAR UPDATE.

A while back I posted about selling a 2008 Fortwo flood car. Everybody on here thought my car was fishy and I never got any offers and then my thread was closed by the man. Well after lots of procrastination I have decided to partner with my neighbor and repair the car. We are starting with...

www.smartcarofamerica.com

Please Disregard the flood title and how dirty the floor was in my car

 

[Qwertyuiop]

Yes PM sent

Can you send to me as well please?

 

[Jo e Lefors]

Can you send to me as well please?

All the information needed for disconnecting the subwoofer I posted in post #13.

 

[Sal marinosci]

Thank you all for all these sub-woofer problems. It has made my cab undriveable , now tomorrow I can go out to the car and fix what no one could diagnose.

 

[Bob Ricewasser]

Thank you all for all these sub-woofer problems. It has made my cab undriveable , now tomorrow I can go out to the car and fix what no one could diagnose.

Reach under the driver's seat and unplug it.

 

[vadsoom]

Have your battery load tested. I recall reading that a weak battery might be the cause of the subwoofer noise.

Oops, I just went back and reread this thread and saw it’s the one where I read the battery solved the subwoofer issue.

 

[Jo e Lefors]

After I installed a brand new Duracell battery in my smart I plugged in the subwoofer it did the same thing as it did before, so a low battery is not relevant with a burping subwoofer.