Unusual sound from underside of car

[magicnote]

Hello i Owners,

My wife and I just took delivery of our i last week and we love the car. I have been hearing a noise that sounds a little off. When I put the car in drive after reversing first, there is dull clanking sound that I hear after few seconds of moving forward. Is anyone else hearing this? I only hear it once and then not again for the rest of that trip.

 

[jjlink]

Yes, I also hear a noise like something motorized is moving/adjusting under the car when just starting to drive after backing up. I don't what its, but I am assuming its normal. Anyone know what is the source of the sound?

 

[oahumiev]

At first I was also wondering what this was but after 2 months of driving it and hearing this sound after each startup, I did some research and it seems like its the air brakes, there's some info in the owner's manual regarding hearing possible noise when first driving, the sound should not be heard after the initial acceleration.

 

[JoeS]

oahumiev, perhaps what you're referring to is the vacuum pump for the power brake booster? Most electric vacuum pumps I'm familiar with are awfully noisy, so I'm impressed if they've almost fully muted the sound and I don't recall hearing it at all on my test drive. I would expect to hear it for a few seconds at startup. In any event, it should be intermittent and also occur for a few seconds after significant braking (and not simply slowing down which uses regen which is what occurs when the brake pedal is first depressed).

 

[oahumiev]

"oahumiev, perhaps what you're referring to is the vacuum pump for the power brake booster?"

Yes, i was trying to refer to the vacuum pump which assists in the braking process, thanks for the proper name. It's not a loud noise but definitely audible thud. Was worried initially since it sounded like I ran over something but now just used to hearing it after first acceleration, don't hear it at all following that.

 

[Wee John]

The noise you are hearing is the self test for the antilock braking system, it does this test the first time you start the car and start moving. If you want to hear the vacuum pump for the brakes you can sit in Park and press the brake pedal three or four times.

 

[magicnote]

Thanks for all the replies! I'm glad other people are hearing the same thing and that is seems to be an expected sound.

 

[iMiEV808]

There are several noises that can be heard while driving an iMiEV. The clunk on 1st drive off after a key start is the ABS self check. A buzz sound from the right rear of the vehicle can be heard every time you press the brake pedal. It is the vacuum pump that builds vacuum for the brake booster. If you pump the brake pedal enough times and deplete the vacuum before the pump can catch up, you'll hear a warning tone inside the vehicle. The noise that sounds like a tram is the AVAS. To hear it with the car standing still, apply the parking brake, put the vehicle into D range and let off the brake pedal.

 

[alohart]

The noise you are hearing is the self test for the antilock braking system, it does this test the first time you start the car and start moving.

Mitsubishi must be receiving enough questions about this noise that they've instructed their salespeople to explain it. Or maybe this explanation was offered by my salesperson on his own volition. I have another car with an ABS system, but I've never heard it perform a similar self-test. Maybe its engine drowns out the sound. But with my i-MiEV, the ABS self-test clunk is very noticeable, so I'm glad that I was told to expect it and that it is totally normal.

 

[iMiEVNZ7]

Yes, The Holden Adventra V8 also does this on startup, and if one has the foot on the brake pedal, you can feel it firm to start with, then on key turn and engine starting, feel the brake go down a bit like the pressure is slightly released, the a push upwards from the system felt through the brake pedal is noticeable. like someone giving the pedal a tiny kick.

We don't notice it if starting without foot on the brake as sound of engine starting is higher than noise of ABS CHeck.

For the iMiEV , yes in NZ it is the same as others have mentioned, noise on start off, then only vacuum pump sometimes.

I am thinking of adding a V8 sound to make the car more quiet to the ears to mask the road noise.

 

[TXCharlie]

I've wondered what that one-time clunk was too - I thought it must be a relay or something. Thanks for clearing that up about the ABS brake test!

I thought that vacuum pump noise was the fake engine sound, since I usually only hear it at slow speed, but the indicator usually isn't on when I hear it.

When I try to make the fake engine sound indicator come on so I can see what it sounds like, it never seems to cooperate. Interesting symphony of little mystery noises at start-up :lol:

 

[alohart]

My understanding from the owner's manual is that the AVAS MIL illuminates only when the ignition is turned on as a test for the MIL and when the AVAS is malfunctioning. So I wouldn't expect it to illuminate when the AVAS is on and operating normally.

 

[iDriver]

My Subaru does this as well. I can hear the THUNK of the ABS test shortly after i start rolling.

Also, if you want to hear the fake "engine" noise/pedestrian warning noise while the car isn't moving, there is a little trick I discovered: Start car, put it in Neutral, pull on the Parking/E-Brake. Now you'll hear the noise. You can even get out and experience the majesty of it from the standpoint of a real pedestrian. Wow!

 

[PV1]

Also, if you want to hear the fake "engine" noise/pedestrian warning noise while the car isn't moving, there is a little trick I discovered: Start car, put it in Neutral, pull on the Parking/E-Brake. Now you'll hear the noise. You can even get out and experience the majesty of it from the standpoint of a real pedestrian. Wow!

Common disclaimer, "do at your own risk".

Honestly, the AVAS is louder inside the car than it is outside. I'd like to just disable it all-together since nobody can hear it, in my experience. Even with it operating, I can still sneak up on people, only for them to finally notice me when the vacuum pump kicks on. Although I do believe that the i's warning sound is louder than the LEAF's. I don't remember hearing the LEAF's at all on my test drive, even next to a building with the window down. I'd like to replace the AVAS with an on-demand warning, like the old EV1 chirp, or possibly the road-runner "Meep Meep".

The initial clunk when you first set off is the ABS self-test. Mine does it, too.