Clyde is in the shop buying batteries for his microphones. The microphones we see later are Shure studio microphones that do not use batteries. Batteries are very rarely used in studio microphones. However, it is possible that he was purchasing batteries for microphones used in his other endeavors such as wireless microphones or even the deposition microphones we see later in the film.
When Shelby is laying down the piano loop for "Whoop that Trick", he is shown first playing it in the middle of the keyboard, but in the next shot, the position of his hand has changed to the bottom of the keyboard, while the notes stay the same.
When Djay and Nola are in the car in the opening scene, the view of the john from their back window shows the window rolled down a good 10-12 inches.
A moment later When Nola exits the car to get into the John's car..the same window is opened no more than one inch.
During the scenes where they are laying down the track for his song, DJAY's hair is slicked back in the recording studio and then messy when he is told to go outside and then slicked back again when he returns to the studio.