Matt,
RC Showcase used to sell carb intake filters that bolted directly onto the Walbro carb. Something like that would work here to eliminate both the intake noise and the flapper noise.

I just found it at Troybuilt. here is the link: http://www.troybuiltmodels.com/items/ZDZCPA057.html
And at Aircraft International (scroll down): http://www.aircraftinternational.com...s/MIntake.aspx

The foam should muffle the sound a bit.

Another option if you don't want to go with these, as they are a bit expensive, would be to get a cheap intake trumpet, wrap a piece of filter foam over the end, and hold it on with an O-ring. This intake will work if you want to try that, and it is very inexpensive. I don't remember which carb is on the SAP-180, but if it is a WA or WT weries carb this intake will fit:

http://www.horizonhobby.com/Products...ickAccessories