buzzing noise when car is off

[emac]

I am familiar with the battery drain issues on the NSX and keep my car on a tender all the time, as it rarely gets driven. It is a stock 97 with no modifications. I keep it unlocked with the keys in the console. Everything on the car works as it should. Alarm, radio, etc.

Tonight I went into the garage and opened the car door and shut it. Then I went over to my workbench and was doing some soldering. It was very quiet and I heard a buzzing noise that lasted about 3 seconds. Sounded like a phone vibrating. I couldn't tell where it came from. About five minutes I heard it again. I heard it a couple more times, and it seemed like it was coming from the engine compartment. Then I didn't hear it anymore. My hearing isnt as good as it used to be, but I swear it was coming from the NSX. Anyone know anything that would do this? Fuel pump relay or some kind of evap pump?

 

[furinax]

How long have you had your car?

To my knowledge it's the evap pump cycling and it is normal. Mine has always done it. It freaks me out sometimes.

 

[alum04org]

No worry. Normal. :smile:

 

[emac]

Thanks guys. I have had the car for years and it has been in the family since about 1999. I just replaced the battery last week as the old one died on the tender. It was pretty old and had been run down a few times over the years when left off the tender.

Honestly, I have never noticed the noise before, but I never hang out with it after I run it. Just was curious with the recent dead battery issue. Thanks again for the replies.

 

[danny49]

They all do that

 

[docjohn]

More like a moan....

 

[silver2002]

Normal, happens all the time - just passing gas

 

[Honcho]

I finally heard this buzz/hum! All these years, two NSXs and I never heard it. After a long drive yesterday I heard the buzzing. I thought I left my phone in the car- it sounded exactly like that.

 

[Old Guy]

On the early pre OBDII cars there is definitely no 'evap pump'. The only actively controlled component is the purge cut off solenoid and when the ignition is off it should be 100% in-active. There is a mechanical two way valve on the fuel tank that connects to the evap cannister. It is normally closed; but, when fuel vapour pressure builds up in the tank it will open to 'pass gas' which will end up getting trapped in the evap cannister. Depending on the conditions in the tank the valve probably fluctuates a bit and might create a vibrating noise. If the tank is close to full there is not much vapour in the tank and there may be no release or a short release. If the tank is closer to empty and it happens to be a warmer day which contributes to the build up of vapour pressure you might get a protracted tank fart.

On the OBDII cars the evap system is more complicated, primarily because of the requirement to monitor the evap system for integrity so there is stuff there to allow the OBDII monitor to periodically test for air tightness; but, there is still no evap pump.

On the 2000+ cars there is an air pump; but, that only operates briefly immediately after start up to facilitate rapid heating of the catalytic converter.

 

[Honcho]

On the early pre OBDII cars there is definitely no 'evap pump'. The only actively controlled component is the purge cut off solenoid and when the ignition is off it should be 100% in-active. There is a mechanical two way valve on the fuel tank that connects to the evap cannister. It is normally closed; but, when fuel vapour pressure builds up in the tank it will open to 'pass gas' which will end up getting trapped in the evap cannister. Depending on the conditions in the tank the valve probably fluctuates a bit and might create a vibrating noise. If the tank is close to full there is not much vapour in the tank and there may be no release or a short release. If the tank is closer to empty and it happens to be a warmer day which contributes to the build up of vapour pressure you might get a protracted tank fart.

On the OBDII cars the evap system is more complicated, primarily because of the requirement to monitor the evap system for integrity so there is stuff there to allow the OBDII monitor to periodically test for air tightness; but, there is still no evap pump.

On the 2000+ cars there is an air pump; but, that only operates briefly immediately after start up to facilitate rapid heating of the catalytic converter.

Yep, it's the diaphragm valve on the gas tank. I find it funny that I've never heard it before!

 

[Old Guy]

Perhaps as your two way valve gets older it gets noisier - like other things in life. My 2000 does not have the same 2 way valve mechanism on the tank. There is a 2 way valve; but, it is in a different location and I am not sure that it has the same function because it is tied in with the Evap pressure sensor for the OBDII monitor. In the tank, replacing the old 2 way valve there is an on board refueling vapor recovery 'thing'. I have never heard any noise from the evap system. Either it does not have the flatulence potential or I just have not been around at the right time.