If you are using a medium to large motorized extractor it should have a ramp speed timer or similar so that the speed can increase from slow to high over a selected period of time. Some of the smaller motorized extractors lack this feature, I would suggest obtaining a router ramp switch, it is a simple rheostat that can be manually operated. Ramp the speed of low to hi over a couple of minutes, leave it on hi for several minutes (3 for mediums, 5 for deeps) then ramp it back down.