Need vibration 24/7 for a few weeks without breaking

[windsmurf]

I don't think that'll create vibrations in the kilohertz range which the OP said he wants...

... and the frequency is not extremely important, but a bit lower is better. The motors I had are something like 10k RPM, but a few thousand RPM would be good if possible.

I was thinking from their original post, the motors were just an offset weight.  10K RPM or 167RPS,   so something under 167Hz was all they were looking for.

I hadn't thought about them trying to make a parts cleaner or a mixer.   I just assumed they were trying to do some sort of basic vibration testing.   

You're right I misread the OP statement as 10Khz....   

[Synthtech]

Go to a drum shop and buy a seat shaker. It’s a subwoofer with a weight instead of a diaphragm  that drummers bolt under the seat of their drum stool and they use an audio power amp to feed the kick drum microphone signal into it to give them the feeling of the kick drum thumping their butt. Feed whichever frequency you want in there up to the maximum that it will handle.