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Resolved 21.5 imac Hums Untill I pick it up??

T

trackbikes

macrumors regular
Original poster
Mar 29, 2011
141
5
I have just grabbed a 2nd hand iMac

It has a really annoying hum , but when I pick it up it stops,

Tried isolating it from the desk with various items, cardboard, books tshirts but it's still there..

Any ideas how to fix it and what's the problem
 
Last edited:
C

cjhorist

macrumors member
Mar 13, 2011
48
0
to me it sounds like it's the desk/surface that you have the imac on. i remember reading a thread about it on this forum. i don't have an imac (yet :rolleyes:) so i can't remember what they ultimately decided, but search for it real quick!

something with loud noise/hum/vibration

good luck :)
 
T

trackbikes

macrumors regular
Original poster
Mar 29, 2011
141
5
cjhorist said:
to me it sounds like it's the desk/surface that you have the imac on. i remember reading a thread about it on this forum. i don't have an imac (yet :rolleyes:) so i can't remember what they ultimately decided, but search for it real quick!

something with loud noise/hum/vibration

good luck :)
Click to expand...

Thats what I thought but it's now sat on top of a book with a soft mouse mat under it and it still makes the low humming sound....strange..
 
John T

John T

macrumors 68020
Mar 18, 2006
2,114
6
UK.
Firstly, it's nothing to do with loose screws, desks etc!!

What sort of a hum is it? Is it a lowish pitch 50/60cps mains hum? From what you describe, this is most likely to be the case. An earthing (grounding) issue is therefore indicated. When you touch the iMac you are effectively grounding it and stopping the hum.

iMacs are connected to earth via their three-pin mains lead. The problem could be a faulty connection to the earth terminal of your mains socket. Are you using an Apple mains lead? Is it in good condition - i.e. not kinked or frayed? Is your mains wall socket earthed correctly? Have you tried the machine via a different mains outlet?

If "mains" hum is the problem, providing your machine has not been tampered with, the fault is unlikely to be with the machine - rather the external wiring.
 
T

trackbikes

macrumors regular
Original poster
Mar 29, 2011
141
5
John T said:
Firstly, it's nothing to do with loose screws, desks etc!!

What sort of a hum is it? Is it a lowish pitch 50/60cps mains hum? From what you describe, this is most likely to be the case. An earthing (grounding) issue is therefore indicated. When you touch the iMac you are effectively grounding it and stopping the hum.

iMacs are connected to earth via their three-pin mains lead. The problem could be a faulty connection to the earth terminal of your mains socket. Are you using an Apple mains lead? Is it in good condition - i.e. not kinked or frayed? Is your mains wall socket earthed correctly? Have you tried the machine via a different mains outlet?

If "mains" hum is the problem, providing your machine has not been tampered with, the fault is unlikely to be with the machine - rather the external wiring.
Click to expand...

Thanks, that does sound possible, I live in spain and the wiring isn't the best in the world! I also have a 3 pin uk apple cable going into a 2 pin euro socket via an adaptor

Although if i just touch the case it still hums and only stops when It is physically picked up..

I'll try some other sockets this weekend
 
qap

qap

macrumors 6502a
Mar 29, 2011
558
441
Italy
i've got a similar problem with my iMac 27", the strange thing is that in front of mac i've got no noise, if I go 2-3 meters from it I can hear a loud hummmmmm, also in the corner of the room the hummm is louder. I think it's a resonance with the hard disk and the walls, it's really a weird thing… i've change 3 tables and no change, if I put the iMac in another room I can't hear anythin, the hummm go away :( (also if the imac is closer to the wall the noise is louder)

For me is absolutely not a grounding issue, if you lift it up the noise go away because you absorb the vibration, infact the imac stand vibrate with the hard disk, try to put your hand on the stand near the mac body… it's a resonance in the room (i've got the same noise with the external hard disk if I put it vertically, like the imac hard disk is).

Try it in another room or hold the stand (near the imac body) with your hands (without lift it up).
(I live in europe too ;) )
 
T

trackbikes

macrumors regular
Original poster
Mar 29, 2011
141
5
After 4 hours of testing lots of different things I have a much quieter iMac.

I am sure it's Hdd related, as you can hear the humming dies away as the disk spins down and starts up as it spins up.

I noticed that the sound also changed when I moved my microphone off the desk, It has a very heavy base and affected the intensity of the hum..

I then moved the mac around in different areas of the desk and once again the intensity changed..

In the middle furthest away from the legs and at the back of the desk it was way worse , sat over one of the legs in was much lower.

It's now sat on in one corner of the desk on 2 neoprene mousemats and although there is still a slight hum it's much less...

So I now am pretty sure it's a mixture of the acoustic properties of the desk amplifying the slight vibration of the Disk.

Thanks for the help and suggestions
 
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