When dealing with musical and audio equipment, you will often find that a hiss, buzz, hum or other annoying form of static will interrupt your signal. This hissing sound can always be eliminated, but the method you should use will depend on where your problem lies, as anything connected to the amplifier may be the cause.
Plug your amplifier into an outlet and turn it on without plugging in any microphones, instruments or pedals. If the hissing is gone, your problem lies with something you connected to the amplifier. If it persists, you may have problems with your amplifier or outlet.
Move the amplifier to an outlet that is part of a different circuit. If the problem is gone, your original outlet may be worn or wired backwards, or you may have too many other electronic devices that emit radio waves, such as televisions or light dimmers, connected to the same circuit. If the problem persists, you will need to replace something in your amp, such as a tube, transformer or power cord.
Plug the cable that will connect your audio source to your amp's input jack and turn on the amplifier. If the noise starts for the first time or is greatly increased from a very faint buzz, your cable or input jack is bad or rusted. Worn jacks can be easily fixed by a friend or professional who knows how to clean and repair them.
Connect your instrument or mic to the amp if no hiss has occurred thus far. Do not connect any pedals yet, even though they would fit next in the order of connections. If the noise occurs only when you adjust a knob on a guitar, it may be dusty or rusted. If there is a consistent hiss, the input jack of the instrument or the instrument itself may need repairs. Test this by plugging in a different instrument or microphone to see if the noise disappears.
If the problem persists, plug in your effects pedals as normal between a guitar and amplifier. Place them as far from your amp and cables as possible and do not stand near your amp. If you have a chain of multiple pedals, it is highly likely that one of your pedals is causing the issue, so remove them, one at a time until the hissing stops. If it does not stop, your pedals may be improperly grounded.
If you believe your pedals may be improperly grounded, ground your pedals by connecting them to a sturdy transformer on a different circuit, if possible. Use fewer pedals, especially if you do not use specific sounds often. Large chains are more susceptible to producing noise.
Replace bad cables or other parts and have a professional make any necessary repairs.