Visible crew/equipment: When Dave wakes up from sleeping on his keyboard in the opening scene, as he straightens himself out and gets up to get himself ready for work, you can see the leg of a crewmember moving around in the glass door that is behind Dave. (00:03:05)
Continuity mistake: When Dave leaves his house for work, there is a skateboard leaning up against the wall by the door and there is an umbrella stand with a lot of umbrellas in it. But when Dave gets back home from work the skateboard is now on the other side of the door in the corner and there are now fewer umbrellas in the stand. (00:03:35 - 00:09:30)
Continuity mistake: When Dave arrives at Jett Records and gives Ian his CD, we see Ian putting the disc into a Bose CD player with no speakers; and next to the CD player is a stack of CD cases. However in following shots, the CD player we see now has speakers that are actually attached to the player itself (and this is the same CD player Ian is using.) Additionally the stack of CD cases next to the player is much higher as well. (00:06:05)
Continuity mistake: When the Chipmunks are running through the lobby of Jett Records, trying to get inside Dave's muffin basket, Alvin and Simon get in but Theodore is still running along trying to get in. As Alvin hangs over the edge to try and grab Theodore, he is alternatively standing on or off of the white material that drapes outside the muffin basket. (00:09:05)
Continuity mistake: When Dave throws the muffin basket inside the garbage can there is a clothing item hanging down off of the kitchen seating area, right next to the bin. However a few shots later when we see the bin, the seating is completely clear with nothing on it. But when the chipmunks climb out the bin the item is back on the seat, hanging over the side of it. (00:09:30 - 00:10:25)
Continuity mistake: Dave throws the muffin basket that he stole from Jett Records into his garbage can; and when we see the front of the can there is a handle visible on the side. However when the film goes back to the garbage can (as the chipmunks climb out of it) the handle is no longer visible on the front part of the can that we see, meaning the can itself has somehow rotated. (00:09:30 - 00:10:25)
Continuity mistake: When Dave gets back home from Jett Records, he throws the muffin basket that he stole into his garbage can. When he does this, as he throws it into the can it causes the clear plastic bin liner inside to come off from around the edge of the bin. But in the next shot the bin liner is perfectly sitting around the whole edge of the bin again. (00:09:35)
Continuity mistake: When Dave gets back from Jett Records he enters his music study, removes his jacket and throws it into a blue plastic box. He then takes his keyboard and throws it outside. Then when he comes back into the study we can see the box again, but now his jacket is no longer inside it. (00:09:50)
Continuity mistake: When Dave gets home from Jett Records he goes into his music study grabs all of his instruments and other equipment and throws it out into his front garden area, in a fit of anger. However a bit later in the film when he discovers the chipmunks (and their singing abilities) he goes back out to retrieve all the items; however now they are all in totally different places to where they were when he threw them out. (00:10:00 - 00:18:20)
Continuity mistake: In the shot when we see the chipmunks climbing out of the garbage can that Dave threw the muffin basket into, we can see an ironing board surface to the right of the screen, with just a few items on it. Later on in the kitchen scene where Dave is chasing the chipmunks through the cabinets with a spatula, a whole pile of paper sheets and addition items have appeared on the edge of the ironing board. (00:10:15 - 00:12:45)
Continuity mistake: When Dave is lying on the couch watching television (before he starts hearing the chipmunks rummaging around in his kitchen) the cushions that are behind his back that he is resting on completely rearrange themselves between shots. (00:10:35)
Continuity mistake: When Dave gets back from work and is lying on the couch, on the counter behind him you can see two jars (one with a green lid and the other with a white lid.) But later when Dave notices the bowls moving across the same counter, the glass jar with the white lid has now vanished. Also the magnets and papers on the fridge differ as well. (00:10:35 - 00:11:50)
Continuity mistake: When the chipmunks are in the kitchen, Alvin gets on top of the microwave and opens up two of the cupboards that are full of food. He opens them up and then stands at the ledge of the cupboard in awe, but in the next wider view of the open cupboards he isn't visible at all and has vanished from the shot. (00:10:50)
Continuity mistake: Once Alvin has opened up two of the food cupboards in the kitchen and all three of the chipmunks are rummaging around inside of them, the items that are inside of the cupboards themselves move about and rearrange themselves without the chipmunks touching them; for instance the items of food next to Alvin as he pours out the packet of Cheese Balls. (00:10:55)
Continuity mistake: Once the chipmunks are inside the food cupboards, they begin to devour everything inside. Theodore is seen chewing off a corner of a box of Lucky Charms cereal and eating the cereal that pours from the hole. But a few shots later when the same box of cereal can be seen, the hole that Theodore gnawed from the corner of the box is gone and the corner is fully intact. (00:11:00)
Continuity mistake: On top of the white cabinets / cupboards that run along the kitchen is a whole row of glass jars, vases, pots, etc. During the whole kitchen scene, the actual jars and pots that are on top of these cabinets move around and rearrange in different shots. In the close-up of Alvin pushing over the packet of Cheese Balls for instance; you can see that the jars and pots on the cupboard above are differently arranged than in other wide shots of the whole kitchen. (00:11:15)
Continuity mistake: Alvin pushes over a packet of Cheese Balls and they fall from the cupboard and into a bowl that is on the kitchen counter. He then cannon-balls from the cupboard into the bowl of Cheese Balls which causes a lot of them to fall out of the bowl, spilling all over the counter. However when Dave walks into the kitchen and spots the bowl, the amount of cheese balls on the counter (around the bowl) is much less. (00:11:15)
Continuity mistake: When the chipmunks are hiding under bowls and slowly moving across the counter, the bowls keep changing location, whenever the chipmunks stop moving. (00:11:45)
Visible crew/equipment: When Dave enters the kitchen and finds the bowl of cheese balls, the chipmunks run and hide themselves under some bowls on the other counter. Then Dave leaves the kitchen and the chipmunks start to move along the counter whilst still under the bowls. The first time the bowls come to a stop (and Dave turns to look, etc) in the close-up as the bowls are coming to a stop, you can actually see the white string that was being used to make them move along; if you look then you can see it more easily to the side of the red bowl. (00:11:45)
Continuity mistake: When Dave chases the chipmunks along the kitchen counter, the mess on the counter keep changing arrangement between shots. (00:12:35)
Answer: No it isn't his voice.