Hi Big B. Thanks for the reply. As per my earlier post, this rumble definitely does NOT seem to be associated with the CPU, case or card fans, which is a different noise entirely, and also 'there' in the background, both physically (whirring) and electronically (low grumble), but is consistent, not too intrusive and actually endurable. The problem noise that I'm dealing with is absolutely definitely associated with IE scrolling, mouse action and video-display related activity. I've found many similar complaints that specifically mention 'Scrolling in IE' on other forums/chat threads. When I disconnect the line-out to the powered speakers (Altec Lansing) the rumble/noise disappears totally (while the fans keep whirring, but not grumbling! :mad: !).. While typing this note, with & without the speakers connected, I realise that the problem noise/rumble is also very subtly audible on each keystroke! :o: (Sort of like the early IBM keyboards where people accustomed to a normal typewriter action could 'turn keystroke sound on', but not as sharp).
As I see it, the only possible explanation is electrical interference of some sort, and specifically related to grounding (otherwise it would be modulated by cranking up the speaker volume). Although I've already looked over all the cabling and connections more than once I think I'm even more certain now that it is originating from the motherboard somehow. I'm going try installing a 'not-on-board' sound card. If the noise is still there I'll strip the system and re-assemble it from scratch. I'll keep you posted on the results. :D