Furnace knocks every 10 secs need to know what is happening

What model number?
What Brand?
Does it knock all the time?
Does it knock when running?
Does it knock at night?
Does it knock during the day?
What does the knock sound like?
Is it a metal knock?
Does it sound like a wood door knock? If it does sound like a wood door knock check the doors because it is cold outside.

More information would be nice if you want any help with this.