It could be a number of reasons. It could be a noisy audio interface, or could be due to the fact that the gain setting is too high and it is picking up room noise. A pop filter would help with some of the sibilant noise, but I doubt it would correct it completely. Samson mics are kinda cheap, and in the realm of microphones, you basically get what you pay for.
MPC 1000 w/ JJOS - Korg ESX - Korg EA-1 - Ensoniq EPS 16+ - Waldorf MicroQ - Roland Alpha Juno 2 - Yamaha TX81z - Mackie CR1604 - random rackmount and pedal effects