Ours did that, or still kind of does. I hadn't got all of mine solved, but it is in fact the foil tape you mentioned, or something along those lines. One little piece will drive you nuts. One of my noises was right where a vent penetrated the duct line. It was right over the bed, so quite irritating. Luckily, I can reach that one, but I hadn't quite got rid of the noise. There is another noise coming from the other duct, but it's a little further up in there at maybe a duct connection. Thinking a piece of tape up in there next will rid of that one.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.