PC making strange noise

[SandSii]

Made my PC about a month ago and its been fine and silent as hell. However, last night I noticed it was making a loud humming noise almost like a faded engine being revved up, like the computer was working really hard (even though it wasnt, I wasn't using it at the time, just sat on the desktop screen) and sounded like it was vibrating.
I quickly turned it off in case it blew up!! and rebooted it this morning and it seems fine. However it is still a tiny bit louder than usual. Could it have been overheating? It didn't seem hot from the dispensed air but it was a hot night and it was on for most of the afternoon (and I only had low fan speeds on).

No way near as bad today but it is worrying me that something maybe wrong. Again, I built it a month ago and have had no problems, haven't moved it to cause a loose wire or anything like that and everything seems to be in place so i'm lost for causes. I panicked last night and quickly turned it off when the smart thing to do would've been to identify where the sound was coming from.

 

[SgtScream]

List your specs. You need to what out what "is a bit louder than usual".

 

[tsnor]

Could be a high quality fan spinning up.

Download a tool like "HWMONITOR" and check your temps when you hear the noise.

If your temps are high use a can of compresses air ($7 at staples or amazon) to blow the dust off the CPU heatsink and out of video card and power supply. (but a month or two since build is early to build up dust)

(do you have an optical drive? Was a disk in it? Sometimes your antivirus will spin up the optical drive and read the disk)