Why does a TV screen crackle when you switch it on?

You didn't specify what type of LCD TV you have, whether it's a thinline or an LCD projection set.

If it's a projection set, there's an item in your TV called a lamp ballast, which is used to ignite the gas discharge projection lamp in your TV so that you can see a picture. This is a high-voltage lamp and the ballast is supposed to create at least three high voltage pulses when it starts up, to ensure the gas in the lamp ignites and the lamp starts up.

What you're probably earing is the three start up pulses, which sould like loud, static electric discharges when you turn the set on.