They all sound slightly different,
Meg especially though.
( Major Turd for tonight only, Thu 28 May 2009, 23:10, archived)

That's cos it's a different chick playing her

( Blue Star was working part time at the 5 and Dime, Thu 28 May 2009, 23:12, archived)

is it a really old episode?
Meg was a different character and the voices were a little rougher.
( Master Of Turnips. Only gays and morons believe in ghosts., Thu 28 May 2009, 23:16, archived)

Season 2/3ish,
of 7 seasons. It's evolved a lot since then.
( Major Turd for tonight only, Thu 28 May 2009, 23:24, archived)