We rented a 20" gas-powered vibrating compacter to tamp the fill (under an upcoming concrete floor) in a new barn last month. Got it for $64 total for a weekend. It's noisy but doesn't beat you up, and is basically self-propelled (once pointing the direction you want). And the resulting compacted sub-floor is darn hard, as I can testify after digging into it to put in drain boxes and lines.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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