ASRock P45XE "system" temperature

Where is this temperature probe?

Recently, I did my semi-annual dusting and now despite seeing lower CPU and VGA temperatures, "system" temperature, (SpeedFan's designation), idles about 5 degrees warmer (43C) and under load, (Crysis, Anno 1404, ect.), it's closer to 8-10 degrees warmer than before (55-60C). In addition to that, it takes it a good 10 minutes to go back to idle temperature when load drops - it used to take 3-4 minutes.

The system is not unstable or anything and the NB is barely warm to the touch when "system" indicates the load temperature so I don't see how it could be that.

My case is well-ventilated:

120mm push in front
120mm pull in rear
120mm pull in PSU (top)
92mm + 80mm push in side

CPU cooler, a cheapie ASUS, keeps my E8400 (3.6GHz OC, 1.22 volts) core temps under 55C, usually under 50C
Accelero Twin Turbo keeps my 4850 (700MHz core, stock memory) "memio" temp under 70C, core never more than 50C

Is this a screwy probe or what?!? I'm not too worried about it as stability is fine but just wanted to ask if anyone knows where the "system" probe is exactly on this mobo.

Thanks in advance