The scream let loose by Donna (Mariska Hargitay) was a stock sound effect. Mariska Hargitay has a naturally deep, husky voice and could not produce a scream loud or high pitched enough for the liking of the director.
Originally planned to be filmed in 3D and actually begin production in 3D, the audience would put their glasses on every time the characters put their sunglasses on and the film would change from 2D to 3D. After two days of filming in 3D they changed their minds due to the complexity of filming in 2D and 3D. This is why there are so many scenes where characters are wearing sunglasses
According to stories producer Charles Band tells on his Full Moon Horror Road Show, he was tasked to come up with a great campaign to promote the film. During a brainstorming session he came up with the idea to have the Ghoulie popping up from the toilet. The idea was a huge success and the scene was then shot for the film after the fact.
The poster for the film ( featuring a Ghoulie popping out of a toilet bowl ) reportedly caused several angry mothers to write letters to the studio saying that their kids were too scared to use the bathroom after seeing the poster.