I'm getting a sort of 'beat' effect from my PC. It seems to have been triggered (or maybe just increased to a level at which I've become aware of it) by adding a new (third) HD.
I'm at my desk, and the PC is on the carpet 3 feet away, at the side of the desk. I can just hear this beat from here, behind the familiar high frequency fan and HD spinning sound. Kneeling on the floor with my ear by the PC case, I can hear the beat distinctly, at about 1 cycle per second. But my real gripe is that directly below, downstairs in the lounge, it's surprisingly distinct. By no means deafening, but it is intrusive. I'm aware of it even while watching TV. This is through carpet, underlay and 2 layers of plasterboard.
I did also have mechanical noise from the fan (which itself may have been due to multiple causes, such as bearings, dust and one loose screw). But I've fixed that, and am left with this pesky beat. It doesn't appear to be anything I can stop by touching any PC panels, or even holding the fan itself. So I assume it's some sort of beat in the air itself, caused by the rpm speeds of various components being very close together? Rather like 'heterodyning' in radio terms?
I'm not sure what the best approach is. Presumably I can take the beat frequency out of this apparently sensitive LF region by lowering the CPU fan speed rpm a bit? I could wire a couple of series diodes in the supply. Maybe as an initial step I should buy a new 60mm CPU fan, which is surely unlikely to be similar in rpm speed to the present one.
Any advice would be appreciated please. Anyone else had similar behaviour?