the volcano 9 isn't the greatest choice for an athlon 2500+ and i'd suggest you run it on thermal if you want a lil reduction in noice when the processor is idling (since the temps will be lower, the fan speed will be lower), though the fan will run on the fast side the majority of the time because the heatsink will not be able to keep the CPU too cool to start with.. keeping it on manual would just be a hassle for you, unless you don't mind keeping an eye on your temps and adjusting the unit as needed, and then keeping at max (in my opinion) would be your best choice of all, since a cooler CPU is a more performant one, though you'll end up with quite a loud heatsink/fan combo that way.
<b>and now for something comepletely different</b>
...<i><b><A HREF="http://bytethiscomputers.sytes.net/site/specs.html" target="_new">system specs</A></b></i>