Now, I know this question has been asked quite a few times, but the results always vary and it appears really dependent on the hw. So: Recently, I have been hearing an interrupted high pitched whistle from the case. It is not too loud, but interrupts when I need to ex. read something and concentrate. It is not a singular long beep, but series of small beeps. When I opened the case, I tried to listen where it goes from; it does not appear to whistle from the electric source; and CPU / Graphics / Net card / Motherboard are too close to each other to properly determine. I tried to listen with a straw, but it always appears to emanate from someplace else when using this method. I tried to dust everything, firm the screws, nothing helped. The issue started about two or three weeks back. I purchased the PC about a year ago and the user have not reported anything similar; the last change was adding a new CPU fan about four months ago. The Rig: Mobo: ASUS M4N78-AM SLV1004 CPU: AMD Phenom(tm) II X6 1055T Processor CPU Fan – Coolermaster Hyper 212+ Evo Ram – 2x2 GB PC26400 AM1 Vga – AMD Radeon 7700 FDD: 16 in 1 apacer sln4123 HDD seagate 250 GB sln E78C Cdrom – DVDRW LG sln 5393 Advice very much appreciated!