Switch mode power supplies, have a tendency to create an induced voltage in metal surrounding the PSU. The high switching frequencies cause by the capacitive effects in the internal transformers are usually the cause of this. You will note this tingling feeling when you connect a laptop which is being charged to your desktop PC. The reason for this is that the laptop PSU does not have an earth, because it is supplied with a 2 wire chord. The secondary side negative usually becomes the earth for the laptop, and the electronics negative is usually 100odd Volts to earth. This is what you may be experiencing. This was more prevalent in the days that we used RS232 to transfer data between P.C.s, one could see the spark when the connectors were inserted, and the casings touched.
This is known as "touch current". Do a google search to get some articles on it.
Theoretically there should be no problem connecting earth to the chassis, however not knowing your machine, I would not say that it will not cause any failures.
If you are connecting the PC to the unit, then the PC usually creates the earth path via the comms cable. Once the PC is connected check to see if there is still this elevated voltage.
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