I have a gas Trane furnace, new in 2004, it has started making a loud clunking noise when it starts up and when the cycle ends. What is this noise, and how do I remedy it?
I have a new filter that I can put in.

Thank You.
Sheri Tavens

new filters are always good,,but you need to get up close and personal,,sitting or standing right in front of the furnace you need to try and determine where the loud clunking noise is? exactly

then let us know

Note the timing of the "clunking" relative to the start of the cycle.

change that filter. You may be hearing popping of ductwork, which is due to a dirty filter among other things.

See if you have a metal frame around your filter and if so see if the filter is secured down, if it is not secured down it is possible that as the air flow starts through the filter the filter raises up and hits the metal of the blower housing causing the clunk and as the air flow stops it falls back to the bottom of the furnace making another clunk