I have the above model desktop. A few months back I noticed the fan started running almost at a higher speed or output. It lasts for less than 30 seconds, then it returns to the normal fan sound. It's loud when it kicks in. Any ideas as to why this is happening and what I can do?

Hello,
I am not inherently familiar with HP PCs but it sounds like your fan speed is being controlled by a temperature sensor on the motherboard. If so, the fan will speed up as the temperature rises and slow down when it start to lower. A normal cause for a temperature rise would be doing something that is cpu intensive (like playing a game). However, once done the temperature should start to lower and the fan should slow down. So, if you cannot correlate any activity to the increase in fan speed then you may have a problem with either the fan, motherboard sensor, and or a poor ventilation problem with the case. Now, poor ventilation is normally caused by dust buildup in the front and rear vents and also the fan blades so make sure your intake and exhaust vents are not blocked and check those fan blades too. A periodic cleaning is also recommended (at least once or twice a year). Hope this helps.