Horn sound at start up
 

Whenever I start my car, there is a funny horn sound. Its right after it turns over and then for about a second the noise stops. Almost like a "kazoo" sound. Does anyone have any idea what this could be from. Its not in the interior and it sounds like its right in the middle beyond the dash. I know this description doesn't really help, but just wondering if anyone has run into this. 1988 928s4, manual. Thanks much.

Maybe a restriction or leak in the vacuum system? the vac system would go through the transition from no vac to vacuum during that time frame. then once the vac equalibrium was reached your noise could stop.

Nothing obvious comes to mind, but something along the lines of what Simon suggests seems likely. You need a partner with good ears and a length of hose to to stand outside the car and try to locate the sound if you can make it happen reproducibly. Listening through the hose while the other end is poked under and around the intake manifold and at various junctions in the vacuum system will probably locate the source. It could be the blue/black one-way vacuum valve near the brake booster vibrating in response to manifold vacuum.

kazoo
 

If not vacuum then maybe exhaust? how many miles, are the cats old or new? just a thought Ray

I know this sound.

It's your starter. The solinoid is sticking a bit, so the starter gear is continuing to spin as it retracts. I think the "kazoo" sound is because it's not terribly well balanced and with nothing to spin against, it "over-revs" and vibrates, thus making the noise. My starter would make this noise from time to time. But then it failed. Not sure if yours is getting ready to fail, but you might consider picking up a new one or a good used one and swapping it when you have nothing better to do.

You can very quickly and easily determine if it is a vacuum problem. Open the hood, find the brake booster, find the little black/blue vacuum check valve on the upper back side of the booster. Unplug it from the booster. Crank the engine and see if the buzz is gone. Plug it back in, see if it buzzes. If so, the buzz is simply the check valve buzzing as the air in the HVAC system in the dash is evacuated. No problem, no further damage.

If you want to stop the buzzing, you can try cleaning the valve by spraying a mild solvent in the end that goes to the booster. This will sometimes stop the buzzing.

Everyone thank you for the assistance. The sound is only momentary. Its only happens when the car is turned over, and once started it quickly stops. Does anyone have a photo of the location of the black/blue vacuum check valve?

I keep the car garaged away from my home. So figures when I take someone with me to check it, it doesn't make the noise!

+1 on the starter response.

Good luck

Glenn

I just opened up my starter, as it was sticing, or not turning at all. Thought I had to buy a new one, but it was actually the arm for the retraction that had come loose, and hed begun grinding off the wires on the startermotor. Perhaps that's the problem here?

It's the starter... for sure. I'll two nights with my wife. If I win, you get her for two nights. :icon501: