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Yo... why dont you try downloading the audio from some clean portion of some sci-fi flicks.... obvious one is transformers but I'm sure there are other robot esque vids out there that could really be awsome if sample on the proper. I have noticed extremely short reverbs obviously can color sounds and if the right reverb is snagged, lottsta things will sound pretty metallic and robotic. Going outside with a mic is a great idea, refreshing actually. Biggggs

record them yourself =]
you'll be surprised by what you can do with a little audio editing, I recorded myself dropping a metal sharpener into a bowl, adding reverb, spreaders, distortion, compressors and so on so forth and the outcome of it was: 'what film did you get that sample from;
you can get something really powerful sounding from something like that, just experiment with it.
Flanger + Feedback is always a good one for machine like sounds aswell

Use delays with full wet and just a few milliseconds of delay time. works wonders

I'm afraid your advice won't get to the op 3 years later but thanks anyway.

Use the sounds from Si-Fi moives.

Formant filtered wobbles + very small delay with a huge feedback = pure filth

go to a junkyard with a bat and mic, smash shit , and granulize it you get some cool sounds

I find down-sampling helps.

def freesound and or getting a recorder and just sample all the machine sounds

Apparently you can use comb filter in massiveto get sounds lie snorch