You have a pulse furnace - my home has two!

Here are some hints:

You could build a box around it out of insulation and cardboard - that should help.

Isolate the furnace from the house structure - if it is up in the attic or bolted to a floor other than the basement slab, insist that the installer isolate it properly - he should have known better!

Make sure the intake and exhaust lines are not tightly attached to the house structure - they vibrate and transmit noise too.

Finally, you will still hear the noise no matter what you do. I got used to it pretty quickly and don't mind it at all now.

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1984 300TD