Don't take anything apart, there's nothing you can fix in there. DC headsets are notoriously reliable and well made. 99% chance it's the plane. Presuming the aircraft are equipped with an intercom, try turning it right off, while still using the aircraft radios. If that fixes it (which I wouls expect), you know where your problem is. Most intercoms have a squelch control. With the intercom on, fiddle it.
There could be other issues of compatibility, with which others here would be more familiar, but it's likely fairly simple to get corrected...