Strange XP 2000 temp change

Well, I'll do the typical intro. I'm a long time reader, first time poster. I'm not a big overclocker (not saying I don't want to, just don't have the time to do it at the moment) however I know my way around a computer pretty well.

My issue... Bought my system about a month ago, bought all the parts and put it all together, except for attaching the heatsink to the board (my buddy did it) I watched him the entire time, no problems of any sort. So I get the system booted up, get everything setup and I find that I'm idling at about 46 C with a case temp of about 34 C. Needless to say I was a little suprised, didn't panic though, it's well with in tolerable limits. On a side note it's a mid tower case with a dual fan PS, a Thermaltake smart fan exhausting and a Y.S Tech 80mm intake. So there's fairly decent air flow.

Now, this is where it gets weird... Was cleaning out the case yesterday, took off the heatsink, cleaned it up, put it back on. Boot up the system... all of a sudden I'm idling at around 35 C, I didn't change anything at all, not even the thermal grease... Ran Prime95 for an hour and it didn't go above 44 C.

Anyone got a guess cause I'm stumped on this one... I have felt the heatsink itself to make sure the thermistor isn't just messed or something, and it is physically cooler than it used to be... Sorry if this is a little long on drawn out, but I know you guys like details and it is my first post

Chris

id guess mabey it wasnt seated on the core 100% and was sticking on something.mabey the heatsink clip.
or a possability your buddy used to much thermal compound and it didnt seat either until u redid it.

use a thin layer applied with razor blade.paper thin.or any safe utensil."for us danger prone people.
isnt unheard of.at least ya didnt put the HS on backwards as many do!even non-noobs.