Thanks Blaze...I need to get under there and have a look around. I'll check around the gas tank for that shield.
It seems to happen most oftern when I'm letting off the gas to shift from 3rd to 4th or when I decelerate quickly from aound 40 mph or so. A few years back I had a Nissan pickup that developed a similar noise. In that case the exhaust pipe was knocking against the frame due to a missing hanger. I doubt that I have a missing exhaust hanger but again, I need to get under there and poke around.
2010 Cobalt XFE
2006 Chevy Colorado 4x4
2005 Toyota Corolla
2013 Kubota M5640 SUD