Condenser - but on SECOND outside wall?

[AverageJoe]

I am building an interior 250 sf room *inside* an existing out-building (sports, bourbon, cigars, music, etc.). I will put a 9,000 BTU mini-split inside the interior room and bought 25' line set to run in the loft above to the outside. I get a lot of snow and the (self-proclaimed) HVAC expert at a local big box said hang it 40" high on the outside/exterior wall. I've read about vibration and am concerned but also like the idea of it being out of the snow and not pouring a base for what this light condenser. However because it is on an outside wall, and my new room will be constructed inside the existing building, would I really feel or hear the vibration or noise from the outside wall? The barn is wood frame on concrete block and the exterior is plywood. Pictures posted and I welcome your expertise

 

[jack stand]

It doesn't take much noise to brake the silence. Just the air movement in a traditional ducting will do that. I'm pretty sure you'll hear something with your proposal but I think it's a good one. You're comfort will eventually win over whatever sounds might bother you at first.

 

[rlitman]

A 9000 BTU outside unit is about as small as they come. It won't vibrate much. So long as you have it on proper vibration isolated wall mounts made for the purpose, I wouldn't worry.

 

[Git]

I have a 24k Mr Slim mounted on the back wall of my 3 stall garage. Stucco on wood framing, and it is bolted to the wall using a wall mount. I literally sit about 5' away. This is a dual head unit and the one in the garage that gets used the most is 18k. I can hear it spooling up at times (very row rumbling sound) IF I really concentrate on it, but it is not a problem on all. If the fan is on high, it makes more noise. I put it up as high as I could and it is pretty much out of the way

 

[rlitman]

I have a 24k Mr Slim mounted on the back wall of my 3 stall garage. Stucco on wood framing, and it is bolted to the wall using a wall mount. I literally sit about 5' away. This is a dual head unit and the one in the garage that gets used the most is 18k. I can hear it spooling up at times (very row rumbling sound) IF I really concentrate on it, but it is not a problem on all. If the fan is on high, it makes more noise. I put it up as high as I could and it is pretty much out of the way

And that's 3x the size of the OP's.