[edgled]

put wd640 in drive 2 and 3. now have a hum that cycles louder/softer continuously, although sometimes after a while it stops. any ideas what this might be and how to fix? this is 2006 mp i have had since new..

[ide3308]

is that a 15k drive? it spins a lot faster than 7.2k drives and you might be noticing that

[CharlesS]

When I first saw the title, I did a bit of a double-take, because I thought you had put WD40 in your Mac.

Anyway, I used to have a G4 tower that did that. I think it's because the machine is slight off balance, and the machine is vibrating slightly as a result. If you can shift things a bit so that the center of gravity is in the right place, it might help.

[cgc]

Are your drives mounted to the sleds securely? Can you rearrange the hard drive sleds into different slots to see if the vibration goes away?

[mikesch1]

My mac pro did that once after i put the processor heatsink cover back on incorrectly. I removed it during the installation of an extra sata cable. I noticed that the cover would fit both ways, but it had a foam pad on the once side that once inserted correctly, i believe dampened some vibration and the hum noise.

The mac has sounded fine, ever since I corrected this minor problem. hope that helps.

M

[nikstar101]

I also found that when putting a third drive in the machine there was more fan noise from my Mac Pro (2009). The drive was an oldish 5400rpm so i doubt it was that, but i have a feeling that once you put the drive in a fan spins quicker to keep the three drive cool. Hence the noise increase.

[mackandproud]

I recently had to return a western digital drive. I was using it as an external backup drive in a firewire enclosure. Very loud hum/buzz whenever the drive spun up. Very glad to be rid of it too.

Maybe try a different brand.