Strange humming noise!

[opie521]

Hi, I am a new member as well as a new Bonneville owner. I noticed shortly after I purchased the vehicle that it has a rather loud humming noise coming from somewhere either behind the back seat or under the car. I don't think it's engine related since it does not change pitch when the accelerator is pressed. I did notice that it does change it's pitch dramatically when I turn on the rear defroster. Not quite sure what this could be, anyone got any ideas? The car is a 1997 SE.

Thanks!
Rob

[azu]

Sounds like the compressor pump for the suspension leveling system.

[myfirstbonnie]

Or fuel pump.

Turn the key on withou starting the engine and see if you hear it. Does it start and then go away, or is it constant.

I am thinking wheel bearing if it only does it when the car is moving, fuel pump if it is heard all the time while the car is running, but not moving, or compressor for levelling system if it does it breifly when the car is started.

[00Beast]

If the rear shocks are going out, the compressor could be running constantly to keep them leveled.

[ptrfair]

If the rear shocks are going out, the compressor could be running constantly to keep them leveled.

I'll second that...from personal experience.

[myfirstbonnie]

I feel we need a little more info to make sure what it is. As I said before, if it is only doing it while the car is moving, I would suspect a wheel bearing. If it comes and goes at any time, I would say the compressor. If it does it all the time, I would suspect fuel pump or the compressor due to leaks in air system.

He says it changes when he turns on the rear defrost...............................my 89 has a cheap fuel pump in it and I can hear the hum pulse with my turn signals. That is what I am thinking here, a cheap fuel pump was put in and it is a loud one, just like my cheapo from Schuck's. LOL

Remember he is talking about an SE (does it have the leveling?)

[opie521]

I will have to check again to make sure, but I'm fairly certain the noise starts when the car is started, and is constant. The rear defrost is the only thing I am aware of as of yet that makes the noise change pitch. I will drive it some more tomorrow and get a better sense for what is happening. Thanks for all your replies!!

[myfirstbonnie]

Open your trunk and see if there is a button and a valve stem by the trunk latch. If not, then you don't have the compressor. You could also check the RPO codes to determine if you have the load levelling, but on an SE I doubt it. Look for code G67 on the spare tire cover. Make sure the VIN on the sticker matches the cars VIN. I think you either have a fuel pump going bad, or there was a cheap unit installed like on mine.

[Skippy1827]

Turn the key to the accessory position, don't start the car. You will hear the humming noise better. get out and go to the back of the car and listen and follow the noise. That will rule out a wheel bearing, if you hear the noise then.

P.S., it also could be humming because it doesnt know the words

[00Beast]

Matt, IIRC only SSE/i's had the aux. air port in the trunk, but SE's could have ELC, even though they didn't have the aux. air.

[J Wikoff]

SE's did not get ELC before 00, I don't think.

[myfirstbonnie]

I am not sure either, but there are several ways to find out. We need to hear from the OP if he even has the ELC.

[opie521]

OK, I just went out and checked a few things. I turned the key on but didn't start the engine. I hear the noise for a few seconds and stops. Once I start the engine, the humming returns and is constant. I don't have the inflatable suspension, so that is ruled out. It also rules out wheel bearing since the car wasn't moving. I'm starting to think it's the fuel pump, I can't really hear the noise outside laying next to the pump, but from the driver's seat that is where the noise is coming from. It also doesn't start on the first try sometimes, so that may also be caused by a cheap and/or bad fuel pump. Whatcha think?

[J Wikoff]

I would be thinking the fuel pump also. Sounds just like it.

[Arriva]

Don't wait too long to determine the cause of the noise. If it is the fuel pump (inside the gas tank) and it requires multiple start attemps before the engine starts it will not be long before the pump will fail completely leaving you stranded. Good luck.

[Bugsi]

I agree with "fuel pump."