I tried running the preamp out to my recover without the turntable plugged into the preamp and still heard the noise. That eliminates the possibility of it being the TT, right?
Right. In this case then it is a problem with shielding or grounding in the unit itself. The wide bandwidth story is something clueless people hope the one they tell it to is gullible or clueless enough to believe. Susceptibility to RFI has nothing to do with wide bandwidth.
Again remember, RFI is radio waves, they are everywhere. You could go out in the middle of Montana, you could shut down all the electricity on the planet. Radio waves come from stars too. What do you think radio telescopes are used for?
So the noise is everywhere but like I said not usually loud enough or at a frequency we can hear. Phono stages and other high gain stages are particularly susceptible. Sometimes with a phono stage you can hear a radio station as clean and clear as if it were a tuner.
That's because in this case it IS a tuner! All a tuner does is take the faint radio frequency noise from a wire we call an antenna, run it through some circuits that select (we say "tune") for a particular frequency, and then modulate and amplify it. A tuner lets us tune from one to another. What is going on here is the amp itself happens to randomly tune some frequency. Just like if you had an old timey tuner or watch one of those old movies where the guy is fiddling with the short wave, it is static, noise, whistles, all kinds of weird sounds, until he gets it tuned to the right frequency. What you have is tuned but not to any frequency in particular it is just stuck between stations so to speak.
This in layman's terms is what's going on. In even simpler layman's terms you got a lemon, take it back, get one that doesn't do that.