weird throbbing noise?

have any of you ever heard a weird throbbing noise out of your computer (not that loud)---it actually feels a little "vibrational" and it "throbs" for about 1 second then it doesn't then it does, etc.....I was thinking it was a power or motherboard/clock speed thing....check out my system listed below and tell me what you think----

also, the thermal diode on this board broke a couple of years ago so i can't tell what the motherboard or cpu temps are----but the heat sink (and surrounding air) is cool to the touch---even after seti all night

sounds like a fan out of whack

power supply?

what about the possibility that a 4 year old 250 watt power supply is not enough?

my system...

cel-tual 1.5 ghz (39 watts as per sisoft sandra)
655 mb pc133 ram (41 watts?---8 watts per 128 mb ram)
ethernet card--5 watts
sound card---5 watts
cd-rw---20 watts?
20 gig 7200 rpm hard drive---20 watts?
floppy drive---5 watts
motherboard----40 watts?
1 cpu and 1 case fan---10 watts?

which is 185 watts (max), but this website: http://www.pcpowercooling.com/maxpc/index_cases.htm

said your power supply needs 1.8 times as much as your system needs....

thus 333 watts---

what do you think?

the vibration sounds like a fan...more power would be good but if it works, it works. i keep thinking i need a better ps too, but everything works, and i have like 4 fans and 6 drives...

i don't know about the power consumption thing, have tried hwdoctor of mb monitor, i might list the realtime power flow through the various slots, etc.

ok thanks---you know it's probably because i just changed the chip and now i'm hypersensitive to sounds, etc....also it could be that since i have intel's stock fan (3200 rpm) on this 1.1A (which is way, way quieter than the two very noisy (but effective) ADDA fans (5500 rpm) on the alpha p3125 heatsink that was previously on my piii 700 @ 933----i can actually here other, unique noises

anyway, i placed my hands on various internal components to see where the largest vibration was coming from and it appears to be either from the case fan (also ADDA) or the cheap little hard drive fan, which i don't think does much cooling...

also, since my thermal diode is not working, do you think it is worth it to get a small temp probe from radio shack or something to check temps----i doubt its necessary since the heat sink is cool to the touch----but i was kind of thinking about the possiblity of heat spikes or something----i do have artic silver thermal grease on it---

the temp probe is a tough call, it may depend on your peace of mind. logically, i would say that if it is stable doing long tasks that there probably is no heatspike problem, whereas if it occasionally goes down it could be heat related; but that is also a sign of undervolting.

i think i am not getting a reliable reading either through the 370gu adapter, i did the same as you and just felt around. also, i have a huge alpha cooler with a 7000rpm fan, so it should be okay.