Steady knocking noise from 5k iMac - should I be worried?

Question

Steady knocking noise from 5k iMac - should I be worried?

I have a late 2015 27 inch 5k iMac with a 3TB fusion drive.

For a few months I've intermittently experienced a steady knocking noise coming from inside the mac. It's a rhythmic noise, always the same frequency - not loud but clearly audible. More of a knock than a click or a tap - I've attached a sound recording.

The noise doesn't appear to be related to how hard I'm working the Mac and I think I've ruled out the fans using some fan control software (cranking the fans doesn't change the noise when it is happening).

I'm assuming this narrows it down to the HDD so my question is - is this something I need to worry about or get checked, or is it normal for fusion drives to make this noise? Diagnostics and DriveDX show no issues with the drive, but I've heard horror stories related to drive noises!

iMac 27″, macOS 10.15

Posted on Jun 24, 2020 6:12 AM

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Answer 1

Jun 24, 2020 10:41 AM in response to dialabrain

Yes IF. 2015 iMacs where available in 3 different storage configurations. With only a Mechanical drive, a Fusion Drive or only an SSD.

Its entirely possible to only have a Mechanical drive in one of those iMacs. iMac (Retina 5K, 27-inch, Late 2015) - Technical Specifications

Storage

3.2GHz
1TB (7200-rpm) hard drive
Configurable up to 3TB Fusion Drive or 256GB or 512GB of flash storage (SSD)
3.2GHz
1TB Fusion Drive
Configurable up to 3TB Fusion Drive or 256GB, 512GB, or 1TB of flash storage (SSD)
3.3GHz
2TB Fusion Drive
Configurable up to 3TB Fusion Drive or 256GB, 512GB, or 1TB of flash storage (SSD)

Or to only have an SSD.

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Answer 2

Jun 24, 2020 6:57 AM in response to SteveSteve1980

2 possibilities I see:

The drive may be failing, if its a mechanical 7200rpm drive its possible it may be failing. If you feel any slowdowns or hangs it would also point to a drive failing. if not, or you don;t have a mechanical drive You have an SSD instead then:
Something in the cooling fan that's moving around with it. Try some compressed air in the vent and see if you can dislodge anything that may be in the fan. The fan is not directly behind the fan, so it may be hard to get the air blast aimed to the fan though.

Those are the only 2 moving parts in that 5K iMac that could potentially be making the sound.

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Answer 3

Jun 24, 2020 9:19 AM in response to dialabrain

Yes I know. If they have a Fusion drive, that would fall under the "mechanical drive making a sound" portion of the post.

And just noticed I said the fan is not behind the fan, what I mean is, the fan is not directly behind the vent.

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Answer 4

dialabrain

Level 10

126,743 points

Jun 24, 2020 9:34 AM in response to SteveSteve1980

Phil0124 wrote:

Yes I know. If they have a Fusion drive, that would fall under the "mechanical drive making a sound" portion of the post.

If? :)

SteveSteve1980 wrote:

I have a late 2015 27 inch 5k iMac with a 3TB fusion drive.

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Answer 5

Jun 25, 2020 2:58 AM in response to Phil0124

Thanks for the reply.

I’ve tried blowing out the vents but in any case had ruled out the fan on the basis that the knocking is always the same frequency independent of how much the fans are blowing – is that a sensible conclusion?

Re the HDD – I’ve not experienced any unexpected slowdowns or hangs and disk scans have revealed no errors on the drive. Wondering if there is anything else I can do to help establish exactly what the knocking is? It doesn’t match any disk sounds I’ve found online (e.g. doesn’t sound like the click of death) and haven’t found an activity that forces the noise to occur which makes me think a Genius Bar appointment might be of limited value (Murphy’s Law dictates that it won’t knock then).

I’m not averse to having the drive replaced but only if I’m confident it’s definitely on the way out – I’d obviously be paying for it as warranty/Apple care is long gone!

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