Excessive rattling noise

When using the vibrator, my machine makes an excessive amount of high-pitched rattling noise, as if there is a small loose piece of metal clanging around at supersonic speeds. I've tightened every bolt down as much as I'm able, to no avail. The source appears to be located somewhere near the tamper arm. Is this normal? If not, what is something I might try to alleviate the issue? This sound is driving us bonkers! Please help!