1) Welcome to the party!
2) Moving to SUPPORT as this is not a development question.
3) While it is possible that this is normal OR a bug ... it's hard to tell if we do not know whether you have a normal installation or a scratch install. So:
when you post, please post your entire configuration including (but not limited to) your installation method and vicidial version with build.
this IS a requirement for posting along with reading the stickies (at the top of each forum) and the manager's manual (available on EFLO.net, both free and paid versions)
You should also post: Asterisk version, telephony hardware (model number is helpful here), cluster information if you have one, and whether any other software is installed in the box. If your installation method is "from scratch" you must post your operating system and should also post the .iso version from which you installed your original operating system.
If this is a "Cloud" or "Virtual" server, please note the technology involved along with the version of that techology (ie: VMware Server Version 2.0.2). If it is not, merely stating the Motherboard model # and CPU would be helpful.
Similar to This:
Vicibox X.X from .iso | Vicidial X.X.X-XXX Build XXXXXX-XXXX | Asterisk X.X.X | Single Server | No Digium/Sangoma Hardware | No Extra Software After Installation | Intel DG35EC | Core2Quad Q6600
4) Test! You should, without question, have a test call run on a regular basis to see if you can catch this in the act. Also check your logs to see if the 3 second is accurate based on the begin/end times of the actual call. May not be a bad idea to check the server load during the moment this happens (ie: does it happen when you are dialing 400 channels but NOT when you are only dialing 50?)