This article lists some common sound problems and offers several ways to solve them. A few of the solutions are obvious, but we've all made simple mistakes like not flipping a switch. If the advice given here doesn't work, determine which device is at fault, then obtain help from tech support at the manufacturer.

No Sound
Be sure everything is plugged into AC power and turned on. (Sorry – had to mention it!)
Be sure that all cables are connected to their proper equipment inputs and outputs.
Put fresh batteries in wireless microphones.
Replace broken cables.
Check for signal presence in each component by looking at the meters or indicator lights. Look for trouble in the first component in the chain without a signal, or in its input cables.
Check all switch positions. Is a mic/line switch set to "line" when it should be set to "mic?" Is a fader down that should be up? Is a microphone not assigned to the proper channels or groups? Are any mute or solo buttons pressed? Is the input trim turned all the way down? Is a wireless microphone turned off? Is phantom power turned on for condenser mics?
Use a headphone amplifier and headphones to troubleshoot the system one component at a time, from output to input.

Distortion
If you hear distortion on every sound source, make sure that the power amplifier is not turned up so high that it is clipping. You might need more amplifier power. Doubling the power increases the SPL by 3 dB.
Make sure that the mixer meters do not reach above 0 except occasionally.
If your mixer output is balanced, +4 dBu, but the device it is feeding is unbalanced, -10 dBV build and install a 12 dB pad between them. Or set the +4/-10 switches accordingly.
A stray wire in a connector might be causing a short circuit which can create distortion. Check inside each connector for stray wires and cut them off.
Clean connectors with Caig Lab DeoxIT.
You might have too many speakers connected to the power amplifier, so that the load impedance is too low for the amp. Remove some speakers and see whether the distortion stops. If so, use another power amplifier for the additional speakers.
If only one microphone is distorting, locate its input trim (gain or atten) control on the mixer. Turn the control down just to the point where the distortion stops, then a bit more to allow some headroom.
If the input trim is set correctly and you still hear distortion, switch in the pad in the mic, or substitute another microphone. Also, replace the batteries in battery-powered microphones.
You might not have enough phantom voltage for a condenser mic. Most of these mics need 18V or more. If you plug in several condenser mics, the phantom voltage might drop too low. Consider using an external phantom supply.

Noise (Hiss)
Be sure that your mixer meters are reaching 0 on the loudest parts of the program. If this is too loud, turn down the power amplifier, not the mixer.
Check that the input gain or trim for each microphone is not turned down too far.
Check that the mixer master faders and submaster faders (if any) are at or near design center.
If the hiss is only from a cassette deck, check that the noise reduction switches are in the position matching the designation on the cassette label. Or you might just have a noisy cassette.
Replace the batteries in battery-powered mics and transmitters.

Noise (Radio or CB Interference)
Install an RF choke, RF beads, or RF filter capacitors at each mic connector in your mixer or stage box. (For more on wireless systems, see Gary Stanfill’s articles on PSW Tech Corner.)

Noise (Crackles)
If a pot crackles when you turn it, try to clean it by rotating it rapidly. Eventually it should be cleaned internally by a service technician. Try cleaning and lubricating products from www.caig.com.
If a mic cable crackles when you move it, replace it with a new cable or a higher-quality cable. Also check the solder connections inside each cable connector.