I'd appreciate if you could help me troubleshoot the behavior of my machine.
It is a "Ralf reference design", 3700AMB with 120mm fan @5v in the back, cool and quiet Celeron 2.4 Ghz and nice Fortron 300W PSU. It also has 3 hard drives (2x160GB Seagate 7200.7 and 1x200GB Seagate 7200.7) that I recently put there - the troubles began after I put the hard drives in (I used to have 2x200GB WD drives in there which were quite noisy at idle).
The problem:
I can hear my computer from another room (downstairs, the PC is on the 2nd floor) and all I hear is some low frequence rumble, like 1 second of noise and then about 0.5 seconds of silence. Turning that PC off gets rid of the sound. I can't hear much in the room the PC is in - and the PC is pretty quiet. There is some subtle noise but nothing like I hear from downstairs.
Any suggestions where to look? I tried disconnecting the hard drives and it seems if I disconnect all 3 then the sound goes away, if I disconnect just 1 then the sound becomes quieter but is still there.
The drives are grommeted using McMaster grommets (note: I've been using those grommets for another machine and reused them here - I hope they aren't single use, are they?)
Could it be that the PC case serves as the amplifier for the vibrations and "converts" quiet 7200 rpm into loud 50 Hz or something?
![Mad :x](./images/smilies/icon_mad.gif)
Any help or suggestions would be much appreciated. I have a lot of hardware at home so I could do some experiments.