On our Forester 3121, the AC vibrated like that and could be fealt just as you mentioned, but it wasn't a DD nest. It was either an out of balance fan, or the fan motor itself had a warped shaft. It was to be replaced, but we sold the motorhome before fixing it. Same exact problem you mentioned. Take the cover off and watch the motor / fan while it's running. Ours had a LOT of movement / vibration.
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.