I see your issue. looking only at the noise issue with the Dell Precision 390 I found this thread
http://en.community.dell.com/support-forums/desktop/f/3514/t/18424381.aspx which has the following advice posted by Xa3r0 that seems to make sense
"...my reply may be worth it for some people with this problem. I am a computer engineer and i bought 1 of these PC's from an auction and i had a very noisy fan with it for a while. a month ago the noise finally got to me so i opened up the case and removed the heatsink off the CPU and i discovered that it was around the wrong way. so i reversed it, put it back together and now the PC is as quiet as a mouse. In fact the AMD machine i have here now which is considered very quiet is actually louder!
To explain in detail: the fan causing the noise is the cpu fan which is not attached to the heatsink at all. it's a large 4-5 inch fan blowing air from the front side of the case through the cpu heatsink. when you remove the heatsink (2 screws, 1 top 1 bottom) you remove the screws with a phiips head (star head) screwdriver, then you open the outer housing like a door from left to right.
when you look at the base of the heatsink (the bit the actaully rests on the cpu) you'll see that 1 of the sides is straight and the other is angled, kind of like this: straight edge --> [ > <-- not straight edge.. face the not straight edge towards the fan and put the heatsink back into place... once i did this, no more noise!. Also, i disabled all SPEEDSTEP options in the bios. I tried doing that before removing the heatsink, no luck..." then continues later
"additional note: some engineers/DC administrators would face the heatsink the wrong way intentionally because these machine were housed in a server environment with inadequate cooling so having the fans run at high speed constantly would guarantee that the cpu remained cooler no matter what state the computer was in which meant longer running PC's... the downside is decreased fan life, but being as robust as DELL pc's are , this hasn't been an issue for mine. I use mine as a server at home with the heatsink mounted correctly and it runs 24/7 so far for nearly a year now and no issues to report aside from the occasional power blackout/brownout

"
Still looking into the swap possibility though