Threshold was set too high. That's why it is best to use good headphones if you're going to use Threshold on any detector. Depending on how good your hearing is you may push the Threshold higher than it should be in order to hear it from the loudspeaker. With some detectors there is no Threshold tone in Disc mode which can really bushwhack you if you don't keep it in mind. You can have a $1K detector, and some kid with a Compadre is going to come behind you and kick your butt because your Threshold is not adjusted correctly. "Silent search" can become "silent killer" of targets if you don't go through a checklist when starting up those types of detectors. If you set the Threshold to a big negative number, the same can happen on the X-Terra's, but a simple 3 second effort of working the menu button will show you where you are at.
As a point of reference with Nugget Buster headphones, volume on headphones down one click from full, X-Terra volume at 30 I can hear the Threshold comfortably at 3. At the ocean with major wind & wave action I push it to 6, but never any higher. But I normally don't use Threshold and leave it at 0(zero) which is my preference. As can be seen in the X-Terra manual, probably the worst thing you can do is turn the Threshold way up and then turn the Volume way down to offset how loud the tone is in your ear. A sure recipe for missing all sorts of goodies!
HH
BarnacleBill