If you hear hissing or static you may need to have the line looked at. Make sure that the serial port rate on your computer is set to 38400 or higher. Settings below 38400 will limit how fast your computer can communicate with the modem and cause slower speeds. Watch out for heat. If you have an external modem make sure it does not get to hot.
Most modems operate better when they are kept cool.
Keep the modem and telephone clear of large appliances. Air conditioners, refrigeraters and other large appliances can cause problems. Try wiping down the telephone jack and phone wire with rubbing alcohol. K56Flex is asymertical, meaning that you can download at speeds up to 56kbps and upload speeds of up to 33.6 kbps. Current FCC regulations actually limit the download speed to 53 kbps.