Attic Fan Noise

It depends on the specifics of the situation. Sometimes it may need isolation (rubber mounts) structural changes etc.

Denis,

The best solution is to get rid of the fan. Studies have shown that the amount saved at the AC does not cover the cost of running the fan.

Ed

I should have also noted that in most cases, such power fans do not help enough on the AC cost to pay for their cost, unless of course the insulation is well below par.

Before reinstalling with rubber pads or whatever somebody might suggest, remove the fan and check it in the workshop for vibration, especially at the angle in which it was mounted in the attic. Replace if necessary.

It might (or might not) be true that the cost of a fan and the energy to run it is greater than the cost of running the AC a little more, but if it's only break even, I would go with the fan so that the attic will not reach

It also adds lifespan to the roof itself, which is a major benefit to the entire structure

BB

It will add a little to the life span, but very little compared to a properly engineered passively vented system and you avoid the possibility of a fan failure and the cost of replacement or a fire.

The fact is, many homes do not have a "properly engineered passively vented system". That's what we are talking about here. These home derive SUBSTANTIAL benefit from fans, and it adds a great deal to the life of the building and the roof. I agree that if you are putting on a new roof or building a new structure, that incorporating passive ventilation is superior.

BB

I agree.

And would benefit even more by correcting the poor pasive system.

It is often possible to make large improvements to the passive system without major changes. It is often necessary to make like changes for a power system to work well.

I agree that passive is not the only answer and in some cases a power system may be the best choice, but it should IMO be considered only after a passive system has been ruled out and in those areas, such as the deep south, where even a good passive system is marginal.