I might be able to answer that, MB, from my own ghost hunting experiences. First of all, what they said might not be completely factual but rather an exaggeration. Even though the cast of Ghost Hunters are, for the most part, critical of claims of hauntings and spend time debunking claims (from watching the shows, they declare close to 90% of all hauntings "unproven" - they even did it with this one with regards to our beloved Collinwood [they never concluded it was haunted]), it's still a show that survives because of ratings. I would not take their claim without a grain of salt. I don't blame them - they're paid for this, and Sci-Fi (or SyFy, which I hate) gets money for this. We're all trying to eat, pay bills, and be able to get stuff we otherwise could not afford with a little extra in the paycheck. Second, "ghost hunters" (I'm an amateur among them), knows from other ghost hunters that a ghost (meaning the spirit/soul/whatever of a dearly departed) cannot effect something beyond human abilities. Humans cannot stomp around like dump trucks; neither can ghosts. Third, sounds, especially in large houses, can be exaggerated because of "travelling sound." Stuff acts like microphones and can enhance sound. Fourth, and this goes with the third, animals living in urban areas are everywhere. When they crawl or walk around, they can be heard, and the sound of their scuffling is enhanced through structures, like a a tuner struck against a surface. When the team climbed through the trapdoor and found only a roof, any animal that might've made the sound would've run (or flew or whatever) off. I once was involved with an investigation in a "haunting" that included the same type of sounds. What caused them? Racoons. In my own house, there were sounds emanating from the ceiling and walls. Ghosts? No - squirrels. Critters are ingenous in making themselves at home in your home.
Ghosts are fun. The episode was fun. DS was fun. Imagine if Stokes, while helping the beleaugered Collins family, had said: "Quentin is not haunting Collinwood. You've got a family of possums living in the rafters." There wouldn't have been a DS for long.
Gerard