many have complained about the headphone jack not making good contact with the plug out. my 396t has just cut out by itself after using the jack, and my girlfriends 396xt has done it a couple of times. the simple way to fix it is to insert the plug a couple of times until it makes contact. you could send it in to be fixed for around 50 or 60 dollars.
since it works again it was not the speaker. mine would go out a lot but it was in my pocket everyday at a lumber yard for about 3 years. sawdust blowing sand and all.the headphone jack works by disconnecting a metal spring when you push in a plug and the sound goes to the plug, when you pull it out it should make contact in the plug but anything in the way (even dust) or corrosion or just a bad contact point and the speaker will not work.
if it happens again just inset the jack and pull it out a couple of times and see what happens
now get back to the radio and enjoy.