Distortion in headset - advice wanted

The audio from the overhead speakers are fine, but the audio from the
headset is very weak. I have to turn the volume to max, but then I get
a lot of distortion and can hardly understand the transmission. The
results are the same from both radios. The problem is not with the
headset, because the results are the same on two different headsets.
The outgoing transmissions seem to be fine also.

Before I take the airplane to an avionics shop, I wanted to ask the
group if I am overlooking something obvious.