I would like to stop an extractor fan shaking my ceiling as it makes a lot of noise. What is the best way to dampen it? (foam, springs etc). Its an exhaust vent for bathroom and is inline with exhaust pipe (not directly fitted) and runs into and out from attic.
The first thing to check is if the fan unit is properly and firmly mounted in the ceiling and that the actual motor/fan portion is tightly secured in the housing. If the vibration is being caused because the fan is unbalanced or the bearings are worn, there is probably not much you can do for it. New fan units are not that expensive and are much quieter than older models. Noise ratings are posted on the units and measured in Sones. The lower the number, the quieter the operation of the fan. Maybe it is time for an upgrade.
You mention "inline with exhaust pipe" which makes me want to ask if it is an inline fan. That type of fan is installed anywhere along the exhaust path route, rather than being mounted on the bathroom ceiling. Those are the quietest you can get, since they are attached to remote structure, and can be installed some distance from the bathroom.
If you don't have that type, and you have the flexibility to replace the existing fan (such as the existing one not occupying an enormous hole in your bathroom ceiling), switching to an inline bathroom is your quietest option. If you already have that, I would look to changing the structure it is mounted to. It could be attached to your ceiling structure unnecessary, and simply moving it to attach to a collar tie or other portion of the roof structure in the attic would help tremendously. If location is constrained, you'll want to explore isolation mounts.