Vacuum!

Ok- Ryan is TERRIFIED of the vacuum. He has never liked it. He cries hysterically when it's on - and is scared to the point where his whole body shakes. I often leave it out so that he can get used to seeing it- but even seeing it makes him very nervous and then all he talks about is the vacuum. He goes up to it and pets it saying "nice vacuum"- but you can tell he's very nervous. Even if he's in the basement, playing with daddy, and I am vacuuming upstairs- he gets very nervous and constantly talks about mommy & the vacuum. I have to check in every so often so that he can see that I'm alright. He's even afraid of the dust-buster (or whatever you call those things). Yesterday- at a mother's group get together- he was playing very nicely in the playroom with the other kids (they have babysitters)- and I was enjoying some adult conversation. Toward the end of the get together- one of the ladies brings Ryan out crying and shaking. She said that they just brought out the vacuum- but hadn't even plugged it in yet- and he totally freaked out. I don't know how to get him past this. We have 3 cats and a dog- so we HAVE to vacuum.

I've tried: 
Leaving the vacuum out so he can get used to it 
Holding him while I vacuum 
Putting him in a safe place where he can watch me vacuum 
We've watched vacuuming videos on youtube (he thinks those are funny- weirdo!) 
We got him a play vacuum (which he loves) 

I have no idea what else we can try.  I feel bad for his future spouse :)