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Hum / Rumble occasionally at idle upon startup.

Posted: Sun Nov 04, 2018 8:21 am
by Goochie
I tried to record this noise on my iPhone a couple of times but cant hear it on playback so I'll try and describe it.

With two small kids we regularly start the engine to get the aircon running whilst we get them into the car. Normally the engine just sits there rattling away like any other cold diesel engine.

However, on several occasions I've started it and it sounds like it is doing something - Its hard to describe but it sounds like its working a bit harder. I'd describe it as a bit of a humming noise or a low frequency rumble.

Its NOT the aircon as the first thing I do each time I hear it is reach inside and turn that off but the noise continues. Maybe it could be a cooling fan noise but the engine is cold at the time so that doesnt make sense.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Tue Nov 06, 2018 10:24 pm
by saeb
So it's a vibration from your description.

Is the vehicle stock, if not what have you added since new?

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Wed Nov 07, 2018 4:02 pm
by Goochie
I'm pretty confident it's not a vibration. Sounds like the change in noise you get when you hear an engine or drive system load-up. A bit like the change in noise you get from a forklift when lifting near capacity etc.

Only mod to date is the ARB bash plate and recovery point but it made the noise before that.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Wed Nov 07, 2018 5:19 pm
by saeb
Not sure mate, hit your dealer up and see what they have to say.

Not the alternator doing its thing. If the battery is low they work pretty hard after about 30 seconds when starting cold.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Thu Nov 08, 2018 11:58 am
by AS82XLT
Does it kind of sound like a jet engine starting up, by that I mean start up humming? I ask because mine does that same thing on a cold start up, a gentle hum / rumble.
I've just assumed that it was the inter cooler getting "charged" up and filling with air and the system loads up.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Thu Nov 08, 2018 1:53 pm
by hoges
Just a long shot but maybe you have an exhaust leak and as it warms up the noise goes away. They don't use a gasket between the ex manifold and turbo, so could be a good starting point.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Thu Nov 08, 2018 7:28 pm
by saeb
AS82XLT wrote: Thu Nov 08, 2018 11:58 am Does it kind of sound like a jet engine starting up, by that I mean start up humming? I ask because mine does that same thing on a cold start up, a gentle hum / rumble.
I've just assumed that it was the inter cooler getting "charged" up and filling with air and the system loads up.
The way you describe yours is the alternator working hard on startup. Mine is identical and pulls just over 100amps on startup so is working pretty hard.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Fri Nov 09, 2018 10:00 am
by AS82XLT
I may have to open the bonnet and have a proper listen to the alternator today.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Wed Jan 23, 2019 8:26 am
by Goochie
Following a conversation with an extremely reliable source I can confirm that this noise is caused by the battery being too low and the vehicle deciding it needs to be charged at a faster rate than normal.

Re: Hum / Rumble occasionally at idle upon startup.

Posted: Tue Jan 29, 2019 11:43 pm
by saeb
Goochie wrote: Wed Jan 23, 2019 8:26 am Following a conversation with an extremely reliable source I can confirm that this noise is caused by the battery being too low and the vehicle deciding it needs to be charged at a faster rate than normal.
Thanks for the followup Goochie, I concur.