Air filter(s) Trane

Hello,
I just moved into a house with a Trane central A/C unit.
The inside air handler is a TWE unit (circa 1998). I found and replaced the filter at the base of the unit but there is a rubberized opening (@ 3x6") with a door and a screw holding it shut.
Upon opening it I found what looks to be some kind of insulation or filter. It is stiff and somewhat yellowed. I'm hesitant to remove the material until I know what it is.
I downloaded the user manual but it does not mention this part. It only says to replace the "filter(s)" every month.
Does anyone have a similar unit or knowledge of what this is and should it, too, be replaced?
Thank you, Robert
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Im guessing ,but it probably is insulation for the furnace and noise reduction
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Thanks, I appreciate the input. I think I'll just leave it alone for now....
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