Your short-wave receiver is a sensitive instrument designed to amplify week radio signals. Unfortunately it will also amplify local man made noise from the lights and machines that can block out all but the strongest of broadcasters. 
In time you will learn to identify the different kinds of interference and where they come from. Most sound like steady roar or buzz all up and down the bands. This comes from fluorescent lights, electric motors, power lines, and nearby power transformers. Sometimes the Noise will appear at the regular intervals, perhaps from a motor that runs at different times.

Other noises appear in bursts, at irregular intervals. This can be caused by electrical switches turning on and off like those found on thermostats or machines. Another common type of noise will sound like a buzz and hum combined and appear only in segments of the band as you tune up and down the dial. Sources for this kind of interference are likely to be television sets or cable television systems in the neighborhood. Similar noises are caused by dimmer switches, and becoming more common, one of switches that there activated by touch.
Now what can you do about local noise problems? In some cases, you may just have to move, or accept the fact the location is noisy. But some problems can be reduced or eliminated, has actually the ones inside your own home. Their at two things to do:

First, build your antenna system with care. Pay attention to keep it away from waste producing sources like power and telephone lines, transformers, and television cable boxes. Of course as a mentioned earlier, antennas should always be kept away from power lines. Run the antenna at the right angles to any noise source you cannot avoid for minimum pick up of the noise. Use shielded lead-in for your antennas so it doesn't pick up stray interference on it's path inside the building. And remember, a good ground for a receiver can help.

The second thing you can do is some detective work to locate a problem sound source. Using a portable radio, tune to the noise and walk around the building or neighborhood to see where the noise is the loudest. When you are next to the noise source it will overwhelm a receiver.

It also may be possible to find the noise by pointing the portable antenna in the direction of the noise. Some portable receivers have directional antenna that allow the signal to become strong when it is pointed directly add that signal source. Once located, you may be able to eliminate the problem, or find ways around it if it's out of a rich.

Some basic repairs of Noise sources are to makes your television sets and their associated antennas or cables are properly shielded electrically. Other devices like some motors or switches that create a spark can be quited by connecting a capacitor across the terminals. Unless you are knowledgeable about electricity, have a technician make these repairs for you.

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