SQL db record shows incorrect date/time once in a while

Has anyone ever heard of this, and what could cause it? This seems to be what's happening. I work on a desk that supports various software, one being a program that utilizes SQL databases and web services. When a user logs a call, the call record is added to the database including the time the call was added: AddDate. Thousands of calls are logged in a month. Approximately 5-10 of those calls show an AddDate of exactly 4 hours (to the millisecond) later than the time it was actually added. I believe the time for the record is taken from the time of the web server. Since the calls opened right before and right after the call with the incorrect time were recorded correctly, it's like the time on the server changed momentarily and was changed back again. Very odd. What could possibly cause this if someone isn't manually doing it? Are there programs or utilities that when run, even if automatically, that will change the time briefly for some reason???? The user knows that the time is different because there is another field in another table that also records an AddDate that shows the proper time and also knowledge from the users knowing when they opened the call. I believe the SQL is 2005 and the web services is the newest MS IIS.