I think I found the problem. My case has a vent above the CPU along with a cone on the inside, presumably to help out the CPU fan. When building the machine, I installed a case fan between the cone and the vent to blow air out, thinking it would be good to draw air out of that cone, pulling heat off of the CPU. I didn't stop to think that the two fans would be very close to each other, blowing air in opposite directions! When I removed that fan, the vibration, and lots of fan noise, went away. The CPU temp is the same as before, and the CPU fan is a lot slower. My motherboard temperature is still high; I definitely need to blow out the dust.

I have two 120mm fans, one in the front blowing air in, and one in the back blowing air out. The one in the front blowing air in also cools my four hard drives.

Here's more pictures:

[URL]http://imgbox.com/g/AABO6gCV4k[/URL]

Glad you found the problem.

OTOH (re: title) what a pity, no vibrations anymore :razz:

[YOUTUBE]r8Ps9310ih8[/YOUTUBE]

[QUOTE=sixblueboxes;333852]When I removed that fan, the vibration, and lots of fan noise, went away.[/QUOTE]

So much for the phrase "no one likes a buzzkill".