Noise investigation continues ....

[davewill]

I have been trying to find the source of a loud whirring/humming noise. On startup, the noise has a sort of grinding component to it and it's very loud. After startup is complete, the noise settles down to just the humming/whirring noise.

At first, I thought it might be the PSU fan. I took the side panel off the case and did a few experiments. The noise is definitely not from the PSU, so I eliminated that. The side of the case where I removed the exterior panel has an interior panel for the fans that swings out. So it's not those fans. I disconnected the fan in the top of the case so it's not that fan.

Localization of the noise rules out the rear case fans.

That leaves the Mobo fan and the CPU fan.

For what it's worth, the mobo fan while spinning looks a little wobbly, kinda like a car tire that's out of balance.

It must be one of those fans.

Any thoughts on how I can isolate which fan it is and how difficult are those fans to replace.

Thanks to everyone who replied to my previous thread.

[edfair]

You can power the system up for 3 or 4 seconds or so with each one blocked from rotating in turn to see which one is the culprit. Doesn't help if both are noisy.
If you can move the fan blade in other than the plane of rotation it may have enough slop to be hitting the housing and that would be reason enough for the noise.
Too many fan types and mounting methods to give a good idea on replacement.

[blue60007]

If I had to take a guess I'd say it's the chipset (mobo) fan. Those things spin pretty darn fast so it's not too surprising to see one die (and sometimes the mobo manufacturers get a bad batch of fans, like the ASUS A8N's had a big thing a while back with the fans dieing). Like edfair said, stick a pencil in the fan (while it's off of course) and then turn it on, after a couple seconds let it go... If you hear it with it stopped, it's not that, otherwise if it goes away you know the mobo fan has gone bad. Usually the manufacture will ship you a replacement fan (especially if it's under warranty still).

[TwoRails]

My two favorite ways to find a noisy component are, 1) use a long bladed screw driver and put the tip on the various components, including HD, and the other end to my ear. This works very well. For items like fans, put the tip on a non-moving part of the fan. 2) use a hose, like a vacuum hose for a car engine much like the screwdriver except it can bend and go places the screwdriver can't. It can do directional finding, too, as you can move the loose end of the hose in various directions to see where the noise is loudest and go from there.