Audio problem: When the Stagehand says "Come on, you're up!" to Susan before she is about to go on the catwalk at Gabrielle's fashion show, the words do not match his lips.
Audio problem: When Susan is on the catwalk at Gabrielle's fashion show, Tom announces what she is wearing, but if you look in the background you can see his lips are not moving when he is speaking.
Audio problem: When Susan suspects someone might be in the house, the seduction music she has put on for Mike is drowned out by the score. When she accidentally hits Mike across the face, the score stops, but the music that was playing in the background has gone. The song in the background before now was music within the show, and it was loud enough to be heard around the house, so we should still be able to hear it.
Your Fault - S1-E13
Audio problem: At the school dance, the students are all dancing at a rapid pace when the music playing is a slow song, indicative that the music was dubbed in later.
Audio problem: When Lynette tells her sons to clean their teeth in the bathroom, the boys turn around and in the mirror you can see Lynette saying the same thing with no sound.
Audio problem: As Carlos is giving his speech at the barbecue, Julie sees Zach and says to Susan "Oh God". After cutting to a shot of Zach and his father it shows Julie and Susan again. If you look to the right of the shot you will see Carlos' face is just looking in front of him and not speaking, but you can still hear him giving his speech whilst he is in shot.
Answer: He was investigating the lead not the case.