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How I Reduced Fan Noise in my G4 Tower
By Mike
Published 12/5/2000

As I noted on the main news page yesterday, I don't think my dual G4/500 is typical as far as fan noise, since my rev 1 G4 and my B&W G3 both use the same fan, mounting and case design but were much quieter. For some reason this new G4 tower was very noisy, something I noticed from day one, especially when sitting on my desktop's hard surface. Last Friday night I decided to see if there was something I could do to easily and cheaply fix that. This page details how I added foam padding between the mounting surfaces of the fan and the metal plate. It may not help everyone, but for this particualar G4, it made a noticable difference, and the system is now much quieter.

Keep in mind although this worked well on my machine, it may not have any effect on others. I'm posting this for reference only as far as what I did to quiet this Mac's fan noise, not a suggestion that you should do the same. (See the required Caution/Disclaimer).

Caution/Disclaimer: Those not experienced/qualified in computer repair should not work inside their machines. Any modifications to your Mac will likely void the warranty. Never work inside a machine with AC power applied. See the owner's manual for additional precautions and instructions. Consult Apple support or a qualified Apple service center first if you feel your G4 is making excessive noise.

Fan noise is affected by several factors, including the fan's blade pitch (angle), RPM, fan type, bearing or sleeve used for the fan shaft, etc. To change these factors however you have to replace the fan. The other factor that affects noise is how it is mounted (structure-born noise). Since the fan in my Gigabit Ethernet G4 was identical to the one in my earlier (rev 1) G4 model and Blue and White (B&W) G3, I decided to provide some "home made" fan isolation to see if that would help.

How The Fan Bracket is Secured in the Case:
The photo below is a picture of the fan bracket mounted in the G4 case (B&W G3 case is nearly identical). The photo shows the two screw locations (philips +) that secure the bracket to the case wall, as well as the four screws (philips also) that secure the fan to the bracket.

Fan bracket in G4

While holding the bracket with one hand, I removed both screws that secure it to the case. (The bracket will drop down after the last screw is removed.) Take note of two tabs on the right upper side of the bracket/bottom of the power supply housing. These are sort of a guide/stop for the bracket during re-installation.

Once the bracket was loose, I removed the four screws that attach the fan to the bracket and left the fan inside the case while I added the foam padding to the contact areas on the bracket. (I never disconnected any fan wiring.)

The photo below shows the bracket back side (where the fan is mounted against). The two metal tabs that I mentioned previously are shown. (*Note* - Applying foam/padding to these two tabs where they contact the metal case might also help reduce noise. You may try this first, since it's easier to do than the fan isolation below. A reader noted this tip alone helped with his case.)

Bare Fan bracket

Since the foam I had was not adhesive backed, you can see the clear RTV adhesive I applied to the contact points (around the 4 screw holes and center hub section).

Isolation Material:
I had some soft (low-density) foam padding laying around so I used this as the material to provide isolation of the fan from the bracket. Adhesive backed felt may have worked as well, although it is thinner, or perhaps some of the soft adhesive backed foam weatherstripping. Some weatherstripping however may be too thick, as you don't want the fan sitting way off the bracket. The idea is to just provide a thin pad/gasket between the fan and metal bracket.

The photo below shows the foam padding I used. I cut this material with scissors into circles, and for the 4 screw mounting areas cut out a hole in the center for the screws to pass through. (Nothing precise required.)

Foam Padding

The photo below shows the bracket with the foam padding applied. (I used photoshop for the image to better illustrate where the screw holes are in the foam.) Even square shaped padding would have worked, as the idea is just to provide padding, not to make sure the shape or edges are perfect.

Fan bracket with foam applied

Now that the foam was applied, I placed the bracket back in the case (properly oriented, tabs up and on the right side), then secured the fan against the bracket with the 4 screws previously removed. Make sure the fan is facing the correct way for proper airflow (the center label on the fan is against the bracket). There's no need to overtighten the fan mounting screws - don't leave them loose of course, but don't go overtighten them to the point where you've defeated the purpose of the isolation.

Once the fan is attached to the bracket, carefully (watch wiring routing) place the bracket back against the case wall, with the two tabs against the stops under the power supply case. (See photo below).

Bracket in Case

Hold the bracket in place and secure it with the two screws removed previously.

My G4 was noticably quieter after this procedure. Again I'm not sure how typical my noisy G4 is, but this mod made a dramatic difference in my case. For other G4 (and other) system related articles, see the Systems page, IDE page, FAQ, etc. links below.

I welcome feedback on this article. [Several readers noted this mod also helped with their fan noise.]

Related Links:

  • Quicksilver G4 Tower Fan Noise Reduction Mods (links also to several Quicksilver G4 noise reduction articles)
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