Q: I am worried about scratching my iPod touch's back metal casing, any tips on cleaning that?

You may want to post this in the iPod touch discussion at https://discussions.apple.com/community/ipod/ipod_touch

The Users Guide says:

Cleaning iPod touch

Clean iPod touch immediately if it comes in contact with any contaminants that may cause stains,

such as ink, dyes, makeup, dirt, food, oils, or lotions. To clean iPod touch, disconnect all cables and

turn off iPod touch (press and hold the On/Off button, then slide the onscreen slider). Then use a

soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don’t use window cleaners,

household cleaners, compressed air, aerosol sprays, solvents, alcohol, ammonia, or abrasives to

clean iPod touch. Rubbing the screen with an abrasive material may scratch the glass.

I would purchases a case for the iPod. It protects the back and make the iPod easily to hold/use.