Any advice for dealing with LOTS of mucus in infant's throat?

Smiling Boy is 2 and a half months and a good and happy baby, overall. But he still has lots of mucus in his throat (since birth), and it sometimes sounds like he is wheezing, especially when he gets tired and starts to get fussy.
It scares DH! Our pediatrician says it will pass and that we can try rubbing his back. I've done that, I've tried burping him and even tried using a NoseFrida to see if I could get some of the mucus out through his nose, but no change so far.

My hairdresser suggested getting a Hepafilter, and I considered a humidifer as well, but I don't understand why either of those would make a difference. Smiling Boy sleeps in a Rock and Play or his swing or Mamaroo, so his head is elevated.

Do any of you have any experience with this?