imac g4 buzzing sound

[sam256]

Got an 800 Mhz 17" imac G4. Opened it up, installed a new battery and an SSD drive (OWC Mercury with IDE->SATA). Reapplied thermal paste; closed it all up. Installed OS 9.2.2

Everything works great except it makes this buzzing sound, almost like the sound a hard drive would make doing disk access (a little quieter and higher pitched but a similar cadence), except there's no magnetic drive after the SSD upgrade. The sound will get interrupted if I click the mouse or do other activities, but if the computer is idle it's fairly constant. I can't tell exactly where it is coming from. If I plug headphones into the headphone jack, i still hear it coming from the body of the machine. Sounds starts about the same time the happy mac comes up. Is there whether or not I have extensions disabled.

Any ideas? I don't mind opening it up again if I need to, but its a bit of a hassle because of the thermal paste, so I'd like to have some idea what I'm aiming for...

 

[Byrd]

Open up again - wires in way of the fan sounds likely

 

[greystash]

I have the same thing and I'm 99% sure its some component resonating. I noticed that it's only affecting my G4 which has PSU issues, the other one is fine. So maybe that would be the first place to look. My symptoms are exactly the same as yours, it makes the most noise during HD/SSD access. My other G4 has an SSD installed and good PSU so the drive type isn't the issue.

 

[ChadVDR]

You know I have a similar issue with many derelict or senile computers. I can hear the sound you’re describing. How many moving parts are left in your G4? Ah, just the fan, right? Therefore…

My theory is that the loose bearings/bushings in an old fan (or dry bearings, since gravity likes to make viscous materials ooze downward) are resonating as they spin. The resonance is directly effected by the amount of current flowing to the fan and that current is directly effected by the computing bits. This is not due necessarily to voltage changes but to the frequency of the work cycles. Think pulse-width modulation.

If you’re feeling experimental, pull the fan and clean it then drop a single drop of watch or gun oil into the shaft of the fan. Just know that gun oil or thicker oils will collect more dust.

I plan to do this to a noisy G5 of mine. Every time I open a file, you’d think the HDD was loading. Actually there is no HDD and the only moving parts would be the many fans and the inactive optical drive.

The only other point for interference would be the speaker. Plug in headphones and repeat the test. Do you hear the sound in your headphones? Does it go away with something plugged in? This would only work if the speaker is truly disconnected whenever something is plugged into the jack but I forget exactly which Apple devices do this.

 

[AwkwardPotato]

My 9600 has a similar issue and the buzzing/whining sound comes from the power supply without a doubt, happens even when the speakers/fans/drives are all unplugged. Clicking the mouse, navigating through menus, etc. change the pitch of the noise. Same thing is much more noticeable in super cheap switch-mode wall adapters.

If you can locate the part in the G4s power supply that's resonating (taking all necessary precautions, of course) you may be able to silence it to a degree with silicone. However there are certain types of silicone you absolutely do not want to use with electronics, I can't remember which ones they are ATM.

 

[sam256]

Thanks everyone for the thoughts and suggestions. I think it has to be some sort of resonance given how it responds to mouse clicks, system activity etc. I'm going to leave it for a few days and see how much it actually bothers me. I do have another imac g4 that has more significant problems (no sound, yellowed case) so I could try swapping parts from it to try to isolate the issue.

 

[ChadVDR]

Power supplies do resonate, though. I don't suppose there's any way to run it with the power supply disconnected? Haha. I'll come back here when I begin to trace my G5 issues to share whatever I find.

 

[macinbot]

SSDs can have a whine/hum when active. Maybe your issue?

ssd access sound - Google Search