If those sounds occur right after you power your PC on, then they are diagnostic sounds form the BIOS. You can count the number of beeps between the pauses to determine what the BIOS is trying to tell you.
Have you had the case open to upgrade or clean the PC hardware? If so, you may have dislodged something. Try removing the memory and any add-in cards and then reinstalling them. Also disconnect and reconnect one cable at a time.