If you have chaff in the exhaust it’s a safe bet the filter basket is not seated properly in the black gasket of the chaff collector. When that happens the filter (the filter is the screen cup) will sag in the gasket opening and the exhaust fan will work to further unseat it by creating a low pressure area between the filter and the fan. When it’s partially out of the gasket the filter can contact the squirrel cage of the fan and make noise or even stop the exhaust fan.
The black gasket which lives in the chaff collector is easily placed in the collector. The issue is getting the lip of the filter basket (the screen cup) to seat in the tiny groove inside the circular opening of the gasket. When it isn’t seated, the filter will tend to pull away toward the bottom especially when the gasket is warm from a roast and has extra weight from the chaff. The gasket is not only softer when you’re roasting, the gasket seems to have less friction.
With the gasket installed in the collector, to seat the filter basket in the rubber gasket I start by pushing the basket thru the large opening, then first work the edge of the filter into the bottom of the tiny groove (‘bottom’ refers to the collector body when it’s installed). With pressure downward to keep it seated at the bottom starting point of the groove I work it into the rest of the groove with downward pressure and the help of a finger nail (a flat blade screw driver might help too- just don’t cut the gasket). When it finally seats you should get audible or at least tactile confirmation as it drops home- a quiet little ‘thunk’ as the rest of the basket seats.
Yeah, way too many words. But if you can weed thru them they may help.