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My new computer makes a noise like a hard disk being accessed - not very loud, and rattling or maybe hissing. The noise changes when I do different things. It is somewhat load dependent - on Windows 7 when the system is completely idle, it's almost gone. With a different operating system, it's there all the time. If I scroll a web page, it is noticable. It gets a bit worse when I do something CPU or IO intensive. The crazy thing is, when I open a terminal window on this PC, log in to a server via SSH, and do something computing intensive there, it also gets loud, although my CPU is barely utilized. Just the updating of the screen alone causes the noise. When I run a game, or a benchmark, it's almost gone.

At first I thought it was the hard disk, but the PC makes the same noise even with the hard disk removed (booting from SSD, or optical drive)! It sounds like it's coming from the power supply or the mainboard. It could be from the electronics, or from the fans.

Some components:

Mainboard: MSI P67A-C43 B3
CPU: Intel Core i5-2500
Graphics: XFX Radeon HD 6870

I never have any crashes, and the temperature seems to be OK all the time. What could it be? Could my PSU be underpowered? Are there any BIOS settings that might help?

(My crazy theory at the moment is that the amount of power that the PC is using at any moment changes rapidly (because the CPU is going in and out of low power states like 100 times a second). That changes the load on the PSU, which changes the fan speed rythmically and creates the noise. That would explain why terminal windows cause the noise, but not games. I don't know if that's plausible or not...)

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If it's a very high, squeaking tone, I'd suspect the voltage converters on your motherboard to be the cause. I know this from one of my computers, especially when scrolling. –  Gene Aug 17 '12 at 8:51

2 Answers 2

Sounds like a fan in your PC has a low quality (or failing) bearing to me.

Most motherboard have some form of PWM (or similar) fan controller on-board, and unless disabled in the BIOS will vary the RPM of the system fans depending on the load/temperature of various components. When fans change RPM due to factors such as system load they can rub against their bearings to varying degrees due to the increase/decrease in applied force.

On a side note, it is not necessarily just the fan bearings that can cause noise - if the blades are damaged or the fan itself is mounted too tight they may rub against the case/cowling. Conversely if the fan isn't mounted tight enough the entire assembly will vibrate.

When these noises occur on the RPM curve of a fan is dependant on a couple of factors such as the type of bearing, weight/size of the fan and how the fan is orientated/mounted within the case.

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This is a great answer. –  CharlieRB Aug 16 '12 at 19:29
    
@Turix: Thanks, the case fans are definitely not too high quality, and I'll check them. However, I think it's still funny that the noise goes away when I start a benchmark... (PS: is there a "not" missing in the third paragraph before "necessarily"?) –  jdm Aug 17 '12 at 7:42
    
Thanks, bad habit of mine that! Regarding the benchmark thing; as you start a benchmark your system load will increase, which will also increase the thermal output of your system. In this case the fans will need to spin faster to keep the "status-quo" thermally speaking - now it is entirely possible for a fan to be noisy when it running slowly and quieter at higher RPM, dependant on the factors I listed above. This is especially true for cheaper fans that aren't designed to work with PWM or otherwise have their speed controlled. –  Turix Aug 17 '12 at 8:37

Turix is correct. The only other thing I would check is to place your hand on different areas of the case when you hear the noise. A number of times I have found loose panels making noise from case frame vibration caused by the fans, optical drives and/or hard drive.

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