Three years after launching a highly critical investigation of rival NBC's "To Catch a Predator" series on Dateline , ABC's chief investigative correspondent Brian Ross has trained his sights on another rival, Fox News, and the relationship between its commentator Glenn Beck and Goldline, a company that sells collectible gold coins that Ross claims are of questionable value. Ross's latest investigation was launched on Nightline Monday night and continued on Good Morning America this morning (Tuesday). It has also spilled over onto the ABC News website, where Ross writes, "The marriage of conservative talk and gold sales appears to make sense -- both have traditionally targeted an audience that is skeptical of the government, concerned about the nation's economic future, and uneasy about inflation and the stability of American currency." A spokesman for Beck told ABC News that Goldline "has an A+ rating from the Better Business Bureau "and we expect any issues that our listeners have to be addressed swiftly and appropriately." A Fox News spokesperson said it has never received a viewer complaint about Goldline. Separately, Beck has revealed that he has been diagnosed with macular dystrophy, a disease that could lead to blindness.