I have a Goodman 90+ furnace with a 3" PVC output pipe, which ends in vertical T.
Here's a side view, with W being the wall:
W W | W-------| W | W
I've always thought that it makes more noise than it should when the furnace is on. It's sounds like a steam pipe at a factory.
If I were to compare it to anything, I'd say it is 3 - 4 times louder than my AC compressor.
Is that normal?