Crack the case open when the buzzing starts and see where it's coming from. Some power supplies have fans that run at dual speeds. Yours may be pumping into overdrive to help with cooling. EQ2 can stress a system and that may be your problem.
I currently run an ATI x1300 256meg which although not being top of the line, it does the job, and for relatively cheap. I would try
www.Newegg.com for hardware before I would try Best Buy. The prices are generally cheaper and they have a much wider selection, although there is shipping involved.