Why is my car making an odd noise?

November 2, 2006 4:42 PM

My '96 Civic is making a peculiar noise when I start it up in the morning.

The noise is a sort of sharp flapping, clicking sound--the best approximation I can think of is the noise you would get if you stuck a piece of typing paper in the blades of a running fan.

The noise starts when I start driving after the car has been sitting around for a long time--so far I have only noticed it in the morning and when I go home from work. It gets louder and faster when I press the accelerator, and becomes nearly inaudible if I ease off. As the car warms up the noise gets quieter, and two or three minutes after I start driving it goes away. The noise sounds like it's coming from the front of the car, from somewhere within or near the engine.

Background: The car is a 1996 Honda Civic, which had its axles replaced last year and will probably need its rear suspension replaced sometime soon. It has had some recent problems with oil leaks. I commute 25 miles each way to work on surface streets and LA freeways.

Is this just an old-car noise, or should I be fearing for the safety of my engine and/or my life?

posted by fermion to travel & transportation (14 comments total)

This was a tough one, but I think I have an idea. It's possible that your hearing the valves tapping while it's warming up prior to their being totally lubricated. You have electric fans, so it's not that.

Is it clicking/tapping? Or flapping, which would be a longer sound?
posted by snsranch at 5:04 PM on November 2, 2006

Is there anything stuck in the fan or fanbelt? I'm thinking twigs or something.
posted by pompomtom at 5:06 PM on November 2, 2006

When was the last time the oil was changed? As well as the coolant....

For those engines, you be changing the oil and the filter every 4-5000 miles and the coolant every 50,000 miles or two years, whichever comes first.

It is more than likely not a serious problem (yet) as it goes away once the car warms up, but I would have it looked at asap, it could be alot more expensive to fix after something serious does happen if you ignore it.....
posted by peewinkle at 5:15 PM on November 2, 2006

snsranch: I'm inclined to say it sounds more like flapping than clicking, but since it's muffled by the intervening car parts it's hard to be sure.

peewinkle: I've been changing the oil on a fairly regular basis (although it may be due again soon.) I also try to check the oil level regularly to make sure it's not leaking again, although sometimes I forget and it gets lower than it should. I'm not positive about the coolant--I'll be sure to check that.
posted by fermion at 5:23 PM on November 2, 2006

This is definately a mystery sound. Just for the heck of it, you should do a little visual inspection and make sure you don't have a piece of newspaper or plastic bag in there.

Also, having re-read your question, I see that you've had you axles replaced. Look around there too. CV joints and boots can be a real mess if not done properly.
posted by snsranch at 5:41 PM on November 2, 2006

Could you have broken motor mounts?
posted by machaus at 6:01 PM on November 2, 2006

It must be valve clatter. If it truly tracks with engine noise and not wheel speed it can't be CV joints or anything else that only moves when the vehicle is in motion (that is, rev the car in neutral - if the sound increases, it must be in the engine). Also, CV joint noises typically don't go away when the car is warm but valve clatter will.

This can be a sign of bad things to come. On the other hand, some cars end up doing this for a long time without incident. I had a Toyota truck that would always clatter until it warmed up and I never had a problem. I put 70,000 miles on it post clatter.
posted by SciGuy at 6:07 PM on November 2, 2006

machaus: how would I tell?

It's definitely not the CV joints--I got my axles replaced because my CV joints were completely shot, so I know exactly what that sounds like.

SciGuy, that sounds very plausible--a Google search indicates that valve clatter can be caused by low oil pressure, so that could be related to the oil leak problems I've had. Sounds like I might need some gaskets replaced.
posted by fermion at 6:24 PM on November 2, 2006

The noise is a sort of sharp flapping

It gets louder and faster when I press the accelerator, and becomes nearly inaudible if I ease off.

Small exhaust leak where the manifold hits the block? Gets tighter when the engine warms?

Definitely not something in the fan as this would not stop after warm up, nor would it, I believe on the Civic which has a fan drive independent of the motor, speed up and slow down.
posted by Pollomacho at 7:11 PM on November 2, 2006

Seconded: this is very likely to be a sticky valve that gets freed up as the engine warms. My (older) Civic had the same problem. I don't think it's worth fixing until (a) it becomes permanently stuck (you'd know, the engine would run very rough) or (b) you're having engine work done that involves taking the head off anyway (like getting a head gasket replaced). When one of those two things happens, I'd pony up (many hundreds) for a valve job or move on to a new vehicle.
posted by RogerB at 10:18 PM on November 2, 2006

Sounds like a wee bit of rod knock to me. Is it worse when it's cold out? Try changing to a higher viscosity oil next time you change it.
posted by notsnot at 4:13 AM on November 3, 2006

You may also benefit from checking your oil level now and adding a bit to fill. It sounds like valve clatter/rod knock, and that can indicate low oil.
posted by kc0dxh at 9:55 AM on November 3, 2006

To follow up: topping off the oil didn't affect the noise much. Hopefully I'll be able to get my mechanic to look at it this week and stop up the oil leaks.
posted by fermion at 12:01 PM on November 6, 2006

Followup the second: I took it in to my mechanic for an unrelated problem, and it was indeed the valves. He told me he could give me an oil additive that would reduce the noise a bit and I could go on my merry way without worry.

AskMeFi is proven right again.
posted by fermion at 5:50 PM on November 13, 2006