Avoid using a line splitter, a duplex adapter, a coupler or anything other than one continuous cable between your wall jack and your modem. Try disconnecting any other telephones, answering machines, fax machines and modems on the same phone number to see if performance improves. A single uninterrupted connection between the jack and the modem often improves performance. Interference can come from the oscillators or transmitters in radios or television sets being near your modem. If you notice problems when a television is turned on or when a radio transmitter is activated, then you have a shielding problem.
Monitors can also emit significant electro- magnetic fields.
This can also interfere with an improperly shielded modem. Never place a modem on top of a TV or video display monitor. If you suspect this type of interference is causing your problem, try orientating the modem and its cables in different positions to see if that helps. Placing an internal modem close to a source of internal computer radiation can induce problems into the modem's phone amplifiers. Try moving the modem to another PC slot to minimize this problem.