I have a 2-year old Trane XL80, two-stage gas furnace, Model TUP120R960K,
installed horizontally in my basement crawlspace. I also have a
relatively new Trane XR13, Model 2TTR3024A, air conditioner with an H-
coil mounted about two feet beyond the plenum. (A 5-ton furnace and a 2-
ton AC - I live in Canada!)

When the fan is running, for heating or cooling, the furnace generates an
annoying rattling sound. I've traced the source to two baffles mounted
on the heat exchanger. They vibrate, particularly when the 2nd-stage
kicks in.

I had a warranty serviceman in today, and he concurred that it was the
baffles that were making the noise and suggested that they could be
removed without causing a problem.

I asked him to hold off, because each of the baffles is clearly stamped
"DO NOT REMOVE."

According to the serviceman, the baffles are needed for vertical
installations, but are not necessarily needed for horizontal installs.

Does that make sense or is he trying to fix the problem at minimal cost
to his firm and possibly creating another major one for me down the road?

I also wonder if the problem could be attributable to the design of my
plenum. Rather than being a large gently curved elbow, my plenum is a
horizontal sheet-metal box measuring 20"W x 30"L x 24"H, on top of which
is mounted an elbow measuring 18W x 16"L x 18"H. This is then reduced to
ductwork measuring 18"W and 8"H.

I wondering if instead of flowing smoothly through gently curved ducts,
air turbulence is being created in the box-shaped plenum, which in turn
causes the baffles to vibrate and rattle.

Sorry for being so long winded and thanks for any help you can provide.

Regards,

Morvin