2010 Mazda3 engine noize shortly after startup

[mscott73racing]

I am noticing a disturbing sound coming from engine after startup. It happens when the initial high idle speed switches to a lower idle speed(5-10 seconds after startup) idling in Park. On other cars this is normally just a small click of a switch type sound, but on my 3 it is much more pronounced, quite loud and sometimes has a grind to it. It only happens after the first start up and is not as bad when warm. I also noticed it during the summer whenever the car was started with the a/c running.
What could this be?
thanks for your suggestions.
Mark

[Zoom Zoom Boy]

I am noticing a disturbing sound coming from engine after startup. It happens when the initial high idle speed switches to a lower idle speed(5-10 seconds after startup) idling in Park. On other cars this is normally just a small click of a switch type sound, but on my 3 it is much more pronounced, quite loud and sometimes has a grind to it. It only happens after the first start up and is not as bad when warm. I also noticed it during the summer whenever the car was started with the a/c running.
What could this be?
thanks for your suggestions.
Mark

Hard to tell without a sound clip. From your description, it does kind of sound like it is your AC compressor engaging though. By chance do you have the vent setting on windows or windows and floor?

[mscott73racing]

I also thought it was the a/c compressor, but since i havn't been using a/c, and the problem is still there, I am wondering if it's something else. I think that the higher revs with the a/c on, and/or the higher revs when cold have something to do with it. I don't remember what the vent settings were in the summer with a/c, but now it is either on windshield defrost, or defrost with floor setting.
I'll try to find out how to post a sound clip of the noise.
thanks

[cujofan31]

Touching on the front defrost setting, i know in my old car (Pontiac Sunfire) that if you set it to only front defrost it would automatically turn on the A/C. This may be the case with the 3 as well because i have noticed in park that the engine does kind of go in a cycle of smooth to rough idle. Turn off any sort of windshield defrost and it should go away, @ least i noticed it to go away.

[Zoom Zoom Boy]

I also thought it was the a/c compressor, but since i havn't been using a/c, and the problem is still there, I am wondering if it's something else. I think that the higher revs with the a/c on, and/or the higher revs when cold have something to do with it. I don't remember what the vent settings were in the summer with a/c, but now it is either on windshield defrost, or defrost with floor setting.
I'll try to find out how to post a sound clip of the noise.
thanks

That is why I asked. It is indeed your AC compressor cycling on and off that you are hearing. Both the full window setting and window and floor defrost settings engage the AC to remove moisture from the air. You are hearing the compressor cycle on and off. Change the vent settings to straight vent on the dash or to the floor only and that will stop the compressor from cycling.

You have essentially been driving with the AC on which robs power from your engine and will also increase your fuel economy.

[mscott73racing]

If that is true, wouldn't the A/C indicator light be on?

[mscott73racing]

I'll be trying various vent settings to resolve this. It's very interesting that the defrost would engage the A/C compressor, and I sure could use better fuel economy.
thanks for the heplful replies.

[mscott73racing]

Indeed, after some vent setting adjustments, it is confirmed to be the A/C compressor making the noise, my question now becomes should the compressor be so loud, and have such a rough sounding engagement?
hmmmmmm?

[Zoom Zoom Boy]

Indeed, after some vent setting adjustments, it is confirmed to be the A/C compressor making the noise, my question now becomes should the compressor be so loud, and have such a rough sounding engagement?
hmmmmmm?

Yah, they all tend to sound and engage like that. I wouldn't worry, but if you are, just ask the dealer to check it next time you're in.

[pacmann33]

If that is true, wouldn't the A/C indicator light be on?

Nah, the AC light is on only when it is providing cooling to the cabin space. It is to avoid confusion for the masses.