Broan-NuTone 509S, 200 CFM 8.5 Sones Sidewall Exhaust Fan

My father-in-law installed our first 509S about 35 years ago in a bathroom that had no fan. It worked very well for probably 10-12 years then seemed to slow measurably. We replaced it with another 509S and it also lasted 10-12 years. Same story with our 3rd 509S and now have installed our fourth. We're never leaving this house so I have already purchased the 5th 509S so that if that model is ever discontinued, we'll have a backup that still fits the hole in the wall. PROBLEM!!! The recently installed 4th 509S is exremely loud. So loud that there is no way to hear the radio while in the shower. My solution was to install a Broan Model SC100W speed control switch. The switch on the fan has been bypassed and the 509S is wired directly to the variable speed switch. This worked wonderffuly for about 3 weeks. Then suddenly the fan speed slowed dramatically and was barely rotating. When turning the knob back to the highest setting the fan worked fine, but again the noise was extreme. It now works only on the maximum setting. Just a slight clockwise turn reduces the fan speed so much that it doesn't even open the flap on the outside housing. I have purchased and installed another Broan Model SC100W switch. Am I expecting too much from the Model SC100W speed control switch in conjunction with the Broan NuTone Model 509S?

I am very happy with the effectiveness of the fan, but it is very loud. Can a variable speed control switch be used to reduce the speed and lower the noise level?

7-31-2020. THIS BROAN 509S WAS INSTALLED 5-29-2020 AND STOPPED WORKING 7-30-2020 - WORKED ONLY TWO MONTHS. IT REPLACED A FAN THAT WAS STILL WORKING AFTER 34 YEARS EXCEPT THAT THE COVER AND TURN-ON KNOB HAD BEEN DAMAGED AND WE COULD NOT FIND RPLACEMENTS. NOW, I HAVE TO SPEND THE TIME, ENERGY, AND MONEY TO FIND A REPLACEMENT AND HAVE IT INSTALLED.

This Broan replaces a Nautilus 509 we bought 20 years ago. ( It is the same, so I think Broan took over the Nautilus product line.) The Nautilus worked great and except for the knob to turn it off and on-which after 18 years wore out, we made a new one. We replaced THE Nautilus as the bearings were starting to make noise and the gasket in the hood for the exhaust lever had begun to disintegrate. But after 20 years??!! It was the only fan we could find that included the exhaust hood and direct vented outside and was pretty much a 'plug and play' with the set up for the Nautilus. We did however, take out the whole Nautilus product and completely installed the NEW Broan which wouldn't have been hard if the directions were followed. (READ THE DIRECTIONS-IT MAKES IT SO MUCH BETTER) If this product holds up like the old Nautilus, when it needs to be replaced in the future, it will be someone else's decision.