I want to convert a portion of my basement into a home theater. There is a wood framed, dry-walled bulkhead in the ceiling running the length of the room (left to right) that contains the main metal return and supply ductwork trunks for the basement and first floor of my house. I have three sources of noise that I’d like to reduce:

1. A supply vent in the ceiling (within the bulkhead area) directly in front of the proposed screen area. How can I best seal off and noise insulate this? I was thinking of using a piece of aluminum and some foil tape to close off the hole in the supply trunk and them maybe a piece of foam on top of that. There is another vent 12 feet or so to the side which will act as the new supply outlet.

2. The boso who finished the basement built the framing for the bulkhead so that it touches the supply and return ductwork trunks. As a result, all of the vibration from the air handler in the unfinished area of the basement is being transmitted to just about all of the wood framing in the finished section. This results in an annoying, audible, low-end hum. Short of tearing that portion of dry wall out (all 20 feet of it) and rebuilding the framing away from the ductwork, or cutting holes in the dry wall at every stud and trying to pry some vibration dampening material between the metal trunk and wood, is there anything I can do? I was thinking I could insert some sort of flexible transition piece between the air handler and trunk so that the vibrations would lose strength before getting to the portion of the ductwork that touches wood framing. Or will the air moving through the ducts still produce an audible vibration? A flexible piece exists on the return ductwork and the vibration on that trunk seems to be less.

3. This is more for the upper floors, but we have a radon reduction system with an exhaust fan attached to the ouside of the house. From that fan there is a pvc pipe that goes up to the roof. The pipe is bolted to the house (through vinyl siding). The hum from that fan is audible from every floor in that corner of house. Is there some way to dampen the vibration that travels between the fan casing and bolts to the house framing?

Thanks so much guysl
All of this humming is driving me nuts!!

First pictures of the area in question are a big help in resolving any problem here on the forum.

For the vibration the real answer is isolation for both the duct work and the vent pipe. You need to add any material that will help in isolating the vibrating mass from the house. I used some rubber mounts to reused the vibration of a fan motor. The added a platform above the ceiling joist that was also isolated on rubber mounts to place the fan on.

I would rip out all the problem duct work and replace with isolated flexible duct work. It is quieter and will not transmit vibration or noise. Also cuts down on the FAU fan noise if you add one or two 90s. Do not know if flexible ducting will work in your part of the country. It is use all the time here in Souther California.