Slow running mc's

If I have multiple mc’s running at the same time and they are slowing each other down, is there any way to fix this? I have one animation of some bubbles and another animation of the background color changing, but when I have them both playing together they slow each other down. If I disable one, the other one and the rest of the movie for that matter, run at their appropriate speeds. Any hints to make them all run together at the right speed?