sagging underbelly/noise in heat duct. plumbing? roof leak?

[wny73]

So i've experienced multiple issues, weird occurences.. It started with hearing a slight drip sound on a heat duct you could hear through the vent. Over the winter I've heard so many strange noises in a bedroom extending into the bathroom and living room. sounds like something in the floor was moving, sounds like banging in the floor or wall adjoining the bedroom/bathroom. the drip sound progressively got louder and could be heard through more vents. Seeing that it started at a vent near an outer wall in the bedroom I kind of assumed it wasn't plumbing. I repeatedly would look in the crawlspace for any signs of water but would see none. Eventually the banging started and some debris would get blown down the heat duct but never any water. There should be no plumbing going through the bedroom or livingroom. Then the noises in the floor started the banging in the bathroom wall floor started got really bad and eventually went away. I hate the damn belly wrap and not being able to see. Ive suspected snow melting and had gotten into the walls because of some sounds that I heard when we had a warmup and a lot of rain over the winter and a lot of snow melted. I see no water damage on the wall or carpet or floor. Over time it seems like the bellyboard sags is multiple areas.Parts of the floor are feeling soft. the only way I will ever figure anything out is pulling the belly material. This feels like a nightmare and I've looked but have no luck finding someone I think would even be down to looking into all this, even if they did it would be a ton of money. Anyone have any similar nightmare experiences?

[wny73]

This is on a 2002 astro doublewide.