04 AC/Heat thumping in dash

[heath223]

Have a 04 Explorer XLT and at times (fairly often) there will be a thumping sound come from in the dash (drivers or middle) I am guessing by the way it sounds it has something to do with the vacuum system or a vent door not closing etc... If you adjust from hot to cold it will go away. This is my wifes auto so I don't know if other things will make it start or stop but I have experanced the hot to cold and it stoped myself. Anyone had this happen and know the cause?

 

[heath223]

Just to be clear this noise happens about every second or so.

 

[majorhavoc]

My wife had this same problem. I turned up the fan to full blast and it went away. SHe hasn't said much if anything about it since.