This is a common problem and usually cause from using different brands of tapes.
Signs of Dirty Heads
The camera can seem like its glitching upon playback with the video and audio. Sometimes the video will have lines across the image, the video/audio will have regular drop outs, missing time code and picture upon playback.
If you have any or all of these issues, You most likely have Dirty Heads.
Why/How does this happen?
Usually this happens from using different brands of tapes. The reason for this is because Different tapes use different types of lubricant and so when you use one tape, That brand of lubricant is on the heads and then you switch brands and use a different tape, The new lubricant mixes with the old and can cause the problems along with artifacts. Now, the reason for the playback and glitches is because when two or more different types of lubricants are on the heads, it makes it difficult for the heads and the tape to communicate.
Solution
Cleaning your heads really helps this problem. But at the same time you do not want to overuse the head cleaner as it wears down your heads. Your best solution to this problem is to Buy One brand and stick to it. I use Sony Premiums and they work great.