Mike
Are you sure the sound you are hearing is not coming from the hard drive? Many consumer hard drives do not use fluid bearings and after time can get very loud. I would try disconnecting the CPU fan then starting up the system to see if it was causing the noise you are hearing. Don’t run the system very long with the CPU fan disconnected or you will damage the processor. Also try starting the system with the power cable disconnected from the hard drive. If the noise is still present then the sound is probably coming from the PSU. Check your video card since higher end video cards have small fans that can become very loud over time.
If your system only has 2 fans it should be very quiet. My system is pretty quite but I have 2-PSU fans, 1-CPU fan, 1-video card fan, 3-case fans, 1-7200 rpm hard drive and 2-10,000 rpm hard drives.
Curt
