It is not normal for a quality power supply. It probably is a cheap single bearing fan so it makes a lot of noise at a very high speed.
The faster a fan becomes, the louder it gets. In cheap power supplies, they put the cheapest and smallest fans they can buy in them, so they grind, make a lot of noise because they are SMALL relative to the high amount of heat generated by the cheap components...cheaper components, have a lower electrical efficiency rating...that means that the amount of working watts is reduced and this translates into more electricity being turned into heat instead.
Working Wattage = Rated Watts X Efficiency, Or...
WW = RW X E, where E is a percentage in decimal percents.
A cheap power supply probably has an efficiency of only 50% of the rated watts. A more expensive, "good" power supply has an efficiency rating of more like 80%. The difference between them, 30%, a reduction in efficiency, directly translates into HEAT discharge.
Since they use cheap, little, single ball bearings in those fans, they have to run at a very high RPM speed to make up for inefficient removal of heat. Thus, a cheap fan will work at over 4500 RPMS while a more expensive fan will operate in the 2500 - 3000 RPM range.
So this is the trade off for buying a cheap power supply. Lower quality components which generate more heat rather than working electricty and cheaper fans which have to work harder to get rid of the additional heat. This results, in a shortened life span on the power supply, and a lot of noise.
If you are displeased, take the computer back or buy a power supply that has a known higher Efficiency rating and make sure the fan in the PSU is a dual ball bearing fan. They even make power supplies with an adjustment nob on the back where you can turn down the RPM speed for a quieter experience.