I have a 99 F-350 that was bought new. It has about 175,000 miles on it. over the past year or so it got louder and louder like a clattering, chatter. Mostly when it is idling and seems to get quieter while driving. The dealership told me it was a torque converter. I have still been driving it because it runs fine and not wanting to put that kind of money into it if I don't have to. The trans. doesn't slip or anything. Is this common with this truck?

 

Yes, it's fairly common to hear the t/c make noise in these transmissions (and also exploders). It will be fixed with the rebuild you'll need sooner or later.