Why's my car making weird humming noise?

July 17, 2010 11:09 AM

Car is making weird humming sound. Can it wait or should I worry?

Car just started making weird noises. I have a '05 Saturn Ion, that's rarely given me a lick of trouble in the past. The last time it needed fixing was in 06, though I can't remember what was replaced (car wouldn't start in cold temp)

Just today it started making strange sounds. It started with a high pitched fast rattle sound, but has changed into a much lower pitched hum. It sounds almost like someone slipped a box fan under my hood. It starts up as soon as I turn the car on, and doesn't seem dependent on speed or turning. I don't hear it as much at higher speed, but that could just be because there's more ambient noise.

Any ideas on what it is and how serious? Of course this happens when I'm about 150 miles from home. Can I go and do shopping and things, or should I limit the amount of driving time? Do I need to take it in right now, as soon as I get home, or can it wait until I get my next paycheck?

posted by Caravantea to travel & transportation (11 answers total)

It could be a loose belt-driven accessory like the alternator. When accessories aren't firmly bolted down they can get out of alignment from the belt causing squeeksband rattles that are proportional to engine speed rather than car speed.
posted by zippy at 11:17 AM on July 17, 2010

If it were me, I'd find a mechanic to take a look-see at it. It might be nothing,... it might be a fuel pump failing. Know what you are dealing with before you decide what to do.
posted by lobstah at 11:34 AM on July 17, 2010

I also think it might be a belt, or maybe a fan. Some belts are more important than others. If it gets louder, you should probably go in as soon as you can. Otherwise waiting until your next paycheck shouldn't be too risky.

Keep an eye on your engine temps while you drive, though, just in case.
posted by twblalock at 11:36 AM on July 17, 2010

Yes, an important point is whether the noise is proportional to engine speed - when in park/neutral, rev the engine slowly up to a faster speed and check the noise changes in either pitch or volume at the same rate.

Also, does it change on quick applications of throttle (when stationary and in park/neutral) - is there a change in sound, like a cough or similar?

I'm wondering if this is an exhaust leak that went from slight leak (small gas emissions in time with the combustion frequency) and now it is a larger hole (a droning from normal engine noise). If you lift the bonnet (or hood for you americans) can you tell where the noise is coming from? Front or back of the engine?

If, when you can hear this noise with the bonnet open, it sounds like air escaping then it is most likely an exhaust leak. If that is the case, there is no need to worry. You can drive safely on an exhaust leak without any problems and just get it fixed when you get home.
posted by Brockles at 11:43 AM on July 17, 2010

Isn't dependent on engine speed or wheel speed? Makes a difference. It'd be odd for it not to change with either. If it changes in pitch when you rev the engine that's one set of things. But if it only changes pitch when you take it out for a drive, that's other stuff. Neither of them should be ignored. Some things can be a lot more expensive to fix if you don't catch them early (like engine timing belts).

Exhaust leaks can be a problem with new engines and emission controls. Modern engine controls depend on the systems working properly. Leaks can cause the engine computer to make it run rich (wasting fuel) or lean (making it run hot). Neither are good for your wallet.

Best bet, have a motorhead friend help you take a look at it. Or pay a local mechanic to give you an estimate (their time is worth it).
posted by wkearney99 at 12:21 PM on July 17, 2010

Thanks for the help everyone. I went back out to test some of your suggestions...and record what I was hearing.

So of course now it's not making a sound at all!

I think I'll still get it checked out, it's due for a tune up, but I won't worry that I'm going to be stranded on the highway halfway to home so much.

Thank you!
posted by Caravantea at 12:43 PM on July 17, 2010

Thinking about the belt comment:

With the engine off and cool give each visible belt a push/tug and make sure it isn't just flopping around in there. Also look for pulleys that don't have belts on them. That's bad, but it's not a major repair. (Repeating advice about watching the engine temp.)

I'd also suggest checking the oil, transmission and power steering fluid. Tranny and PS tend to cause whining noises if they're low.
posted by Kid Charlemagne at 1:09 PM on July 17, 2010

Another tip with belts, look for signs of wear. Both on the belt edges and also on all of the engine pulleys. Once place or another will usually show wear marks or gunked up shavings shredded from the belt. There generally shouldn't be any ragged edges to the belt or fresh wear marks on the pulleys.

With any mechanical system (and not just cars), new sounds are not your friend. They generally mean something that was working OK before is not working now. Catching the failing part(s) early is almost always less expensive. Yes, it's a hassle when the sounds aren't repeatable. But don't just ignore it. It's been a while since you've had the car looked at, perhaps it'd just be a good idea to have any overall check done on it. Better to know what needs fixing ahead of time, rather than getting stuck.

You do have road coverage, right? Towing ain't cheap.
posted by wkearney99 at 1:41 PM on July 17, 2010

Open the hood, start the car and listen. Is the noise coming from the belts and pulleys? With the car running, turn on the AC. That'll trigger the electronic cooling fans in front of the radiator. Is the noise present now?
Because, basically, you do have a pair of box fans under the hood. There are two electric fans in a plastic housing that pull air over the radiator and AC condensor. If one of those fans is bad, has a broken blade, or has debris in it, it'll sound like a crappy box fan.
Where are you located, by the way? If you check on iATN.net, you can find a reputable shop in your immediate area.
posted by Jon-o at 1:44 PM on July 17, 2010

Drove the car around a bit more and the sound came back, did some testing and it looks like the air conditioning is the culprit. No air conditioning, no noise. Air conditioning...low humming noise.

So, Jon-o, it sounds like you could be right about the box fan.
posted by Caravantea at 5:09 PM on July 17, 2010

I would agree with jon-o (actually I find I agree with Jon-o on car stuff a lot) with the news of your last post. Good news is that you can probably replace the fans with junk yard models pretty easy. I don't know if it is true with Saturn but most manufacturers use the same stuff across a wide range of models like cooling fans so chances are you can get cheap ones out of a junkyard since oem parts are going to be pricey. If you are mechanically inclined at all changing out these fans can be easy (can be hard depending on how good access is).
The other good news it is an optional thing and you can usually go a good long while with faulty fans-just watch your temperature gauge and if it is getting hot turn of the ac. or don't use the ac in the first place.
posted by bartonlong at 9:59 PM on July 17, 2010