A fan might do that.
I built a machine last year using only a few old components. NEW...Mobo ( DFI NFII 400-AL),1GB DDR RAM,Processor (Athlon XP 2200+) Power Supply (?..mid-range...I don't remember) ,2HD's (both WD caviar series 20GB and 40GB, about 2 yrs old). It's not the quietest machine, but it's not overly loud either. I rarely, if ever, turn the machine off..except for the ocassional restart. I noticed recently(it could've always been happening), rather than a consistent whirring/purring sound, it seems to make sounds like it's speeding up and slowing down (it's hard to describe..lagging..maybe? slightly louder, then quieter??). Hopefully, you get the picture. Obviuosly, the only noise could be coming from the PSU or the CPU fan,although the latter is reasonably quiet. When I notice the noise, I'm lying in bed , so the machine is not in use..only the usual programs running..ie AV, firewall, antispyware...nothing too CPU intensive. My questions..Do you think my PSU could be going out? or could it be the CPU fan burning out? Temps are pretty stable and normal. I don't notice any performance problems at all..the machine is really quite fast and stable. I don't think it's anything major(I hope), but it bugs the H*%! out of me, as I lie there. I really don't notice the lagging sound when I am using it, and I do some CPU/RAM intensive stuff As I write this, it's purring like a kitten (well,a Cat..large,domestic).Could my CPU fan just be kicking in to adjust temp. changes. I realize this is a tough question..hard to diagnose without being here. I live in WI and it's friggin' cold, so the heat kicks in throughout the night. My machine is not real close to the heat source, but could that be why the CPU fan could be trying to adjust temp, becauase as I said the machine is not in use. Any ideas or thoughts would be greatly appreciated! Thanks in advance!