When any hardware accelerated application is rendering a frame (or many of them) a very short noise is coming from my speakers. This can be a game, a WebGL application or XBMC. When the application/game is rendering many frames per second (like most of them do) the noise is a continuous buzzing that gets higher pitched with higher framerates. This applies to Linux and Windows, so I'd assume it's a hardware problem.

The current hardware in the PC is:

• CPU: Core2Quad Q9550
• GPU: Radeon HD 5770
• RAM: 2x2GB DDR2
• Motherboard: Asus P5QLD PRO
• PSU: be quiet! Pure Power 530W
• Screen and speakers: Old 720p LCD TV connected via VGA and aux cable

Muting the TV stops the noise, muting Windows doesn't.

I tried replacing the PSU first (used a Tagan 700W PSU before) because I thought it was a power problem. It wasn't. I tried replacing the motherboard (used a ASUS P5B SE before) next because I thought it was a sound card problem. It wasn't. I tried the GPU in a different PC because I thought it was a broken graphics card. It worked perfectly fine in the other PC. I thought it might be interference, but moving the audio cable around changes absolutely nothing.

I tried using an HDMI cable instead and that did work, but is not an option since my TV has only one HDMI input and I need that for my PS3.