I need to replace a bathroom extractor fan in a family members house. Do these thing tend to be of similar sizes, the current model looks affixed to the ceiling over the shower. I assume there is tubing attached to the top of it, but the fan is dying, and making large amounts of noise which sound like rattling bearings. It is linked to the lights and has a set delay for a few minutes after the light goes off, is this a function of the fan itself? Which model would people recommend for quietness,, and for simplicity of a straight swap?