Hi Phillip,
Which two cameras specifically? Can you let us know what the frame rate and video format was? If they’re dramatically different, you may need to adjust the Speed of 1 of the clips (usually the B camera) and hand sync the clips. One may be faster or slower than the other. If your “B” clip is selected in the FCP Timeline, the keyboard shortcut is CMD+J to adjust the Speed. Next shoot, you may want to make sure that the camera settings are matched as close as possible and feed the audio to both cameras. For example, we have two sets of Sennheiser wireless. One transmitter is on the subject and we use two receivers, one on each camera, to transmit the sound to each camera. This makes it easy to use Plural eyes or to hand sync. I put a clap at the head and at the tail of each shot. When you turn on Audio Waveforms in the Timeline (CMD + Option + “W”), it makes it super easy to visually see where the spike occurred. Sometimes I’ll put a marker on the clip at the spike to make it real easy to line up with Snapping turned on in the Timeline (keyboard shortcut “N”).