Synch audio-powerpoint slides in Captivate

Hi! I have a problem with a file. Hope you have a solution. I converted Powerpoint slides and added audio to a Captivate project. It is more like a video playing with audio on one slide in Captivate and no buttons nor progress bar because the client wants the course to be very limited in options of viewing. Everything seems to work fine and works fine but when I publish or preview HTML, if I multitask and work on something else and have the course playing in the back, the audio goes in one speed and the slides in another one like if the slides show in a more slow speed so the audio looks like it's not synched. Of course if a learner does not multitask and focus on the course this does not happen but if by any chance they get distracted they may feel the course is not ok and get confused. Have someone experienced this? Thanks.