We have Leviton Decora switches throughout our house. Some of the lights flicker, and have since the house was built 4 yrs ago. When they flicker the switch makes the same sound that it does if, when the light is on, you press the "off" side of the switch, but not firmly enough to turn it off. Are these switches defective? Also, what do I press where it says "press to release wire"? Thank you.

Several questions here.

1) Lights should not flicker and switch should not make sound (or get unusually warm)
2) You should not have to 'press hard' to get switch to turn off.
3) Are the switches defective. YES. Remove and replace with ordinary toggle switch and see if flickering and sound-making continue. If problems continue, maybe local electrician should assess problem on-site.
4) Press to Release. You are speaking about wires connected on back of switch using 'quick-connects.'
Wire is pushed into a hole where wire is wedged against brass spring and held tight.
To release wire there is usually a hole or slot next to wire. Push small screwdriver into opening. Usually you have to push screwdriver very hard using one hand while other hand holds switch. Then use your additional hand to pull out wire. Or you can clip wire off and then strip back insulation and start fresh on new switch.
5) Builder electricians sometimes buy super cheap brand knock-offs that are not UL rated. Do not think all Leviton products lack quality. Buy new switches at local home center, and new switches will work fine.
6) When replacing switches, pay attention to screw-color that sits next to quick connect. Take a photo before removing all wires.
Screw colors tell electrician how to wire a device, and you can post new question at fixya, or add a comment for specific help.

7) Resources:
http://waterheatertimer.org/How-to-wire-Cooper-277-pilot-light-switch.html
http://waterheatertimer.org/How-to-twist-electric-wire.html

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