Forum:Voices in Polyjuice Potion?

SO HERE'S THE PROBLEM:
When you drink polyjuice potion, does your voice change to that of the person you are impersonating?

Examples:

1. Chamber of Secrets- Harry and Ron DO NOT get Crabbe and Goyle's voices

2. Goblet of Fire- Barty Crouch, Jr. DOES get Mad-Eye Moody's voice

3. Deathly Hallows- Seven Potters DO NOT get Harry's voice

4. Deathly Hallows- Hermione DOES get Bellatrix's voice (I think?)

Can anyone explain this?