Banging air damper

The exhaust hood for my stove terminates in what looks like a big dryer vent with a similar hinged cover except it is 8" diameter pipe feeding it rather than the more typical 4" from say a dryer. Where it is, there are sometimes some eddies caused by the wind and the thing bangs. Gravity isn't enough to hold it shut. There is no foam or felt on the edges, probably because it would also trap any grease that got by the filters (I've never noticed any there, but I'm guessing it could be a problem). So, was wondering if there are any ideas. One I had was to add a small weight (maybe just a magnet). I think the blower motor is plenty strong enough to still blow the thing open.

ANyone have any other thoughts or suggestions? It's time for some experimentation...looking for ideas and pitfalls I may have overlooked before I start.

Many range hoods have a damper on the unit itself so the second one would not be needed, but if yours did, you would have to check yours to be sure it was not removed.