Active attic radon fan in place for a couple of years. Normally, can hear a little bit of air moving from gap between concrete slab & foundation wall. Steady, low volume noise. Liquid on gauge has normal differential, 1.4.

New noise coming from pipe about one foot above slab.  Sounds a bit like sucking air with a straw as your drinking glass empties. Not quite the same sound, but similar.  Also sounds a bit like a bee hive. Pretty loud, can hear it 20 ft away.  After a bit, volume dropped some.  Any thoughts? Thanks.