[Kevin Kuehn]

That seems really strange. I think someone mentioned earlier that most service grade sweep generators won't produce a pure sine wave, and also there's no way to get an accurate frequency reading if there's any frequency modulation(sweep) turned on. So it's very possible your counter is picking up on a false harmonic. Another thought is it's possible that your local oscillator is producing something other than the correct IF frequency. But if the IF slugs are back to their original positions that's not very likely, not unless someone else had that thing incorrectly aligned long before you got your hands on it. But at any rate the fact that you're getting the best video and sound with a single peaked frequency response is very strange.