The most common cause of this is dust, debris or contamination on the heads.
Firstly, it's extremely important that you use only DRY LUBRICANT type DV tapes on the Canon branded camcorders.
Different manufacturers design their heads to be used with either Dry or Wet (coating lubricant type) tapes - NEVER BOTH. Canon is DRY type.
Consumers are led to believe that they should be using well known branded DV tapes, such as Sony. This is fine, if your camcorder is a Sony. However, you should NEVER use Sony tapes in your Canon
- Sony tapes are of the WET type.
So, the question is, "Are you currently using Dry or Wet type tapes, or a mixture of both?" If you have used either a WET tape, or a mixture of both in your Canon, then this may have contaminated your heads.
If this is so, then don't panic - simply run a special Head Cleaning cassette (for Dry tapes) in your Canon for no more than 5 secs. Note: your heads are very delicate, so only run the cleaning tapes for a few secs at a time.
Also, try to avoid recording over the cassette too many times, as the quality will sometimes degrade each time.
An example of the Dry tapes are the Panasonic ones (Myself and other Pro Videographers often use Panasonic Prof, Studio or Master Quality tapes, as these are some of the better quality Dry tapes on the market).
As your XL2 is a Pro Camcorder, I recommend you stick with Studio quality (or higher) cassettes.
See this link for Dry DV tapes: http://cgi.ebay.com/Panasonic-mini-DV-digital-video-cassette-AY-DVM63SQ-5pk-/170645949017?pt=US_Camcorder_Tapes_Discs&hash=item27bb4a8a59
See this link for Head Cleaner cassette: http://cgi.ebay.com/MiniDV-mini-DV-Panasonic-Head-Cleaner-Cleaning-Tape-/220683036059?pt=US_Camcorder_Tapes_Discs&hash=item3361bbe59b
If the problem still exists after head cleaning, then suspect either a faulty cassette (most likely) or damaged heads requiring service.
Let me know how you get on...
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