I’ve got a tin-ey metal rattling sound that only periodicly comes from the engine block itself. it sound like someone is shaking a coffee can with a penny in it. It almost sounds like something is vibrating. (05 ford escape 6cyl over 100K)
I’ve watched videos of people on youtube that have a knock, and it doesn’t sound like that.
It is possible you are getting a pinging sound from knocking.
Try running premium fuel and see if it reduces. Not a solution but will at least help you diagnose the problem.
Pinging is early detonation of fuel before its supposed to. Premium fuel is more stable against detonation(from compression) so this does not occur. That is why its spec’ed for high performance motors which use high compression to achieve more power.
Quick google for you>>>> http://www.escape-central.com/1forum/showthread.php?threadid=32870
+1
Many people would describe the sound of engine ping as similar to a pebble in a tin can.
So, like Andrew, I do think that this is a possibility.
While using premium gas may indeed eliminate the pinging, it will not eliminate the source of the problem. If your spark plugs are overdue for replacement, that is the first area that I would work on.
If the spark plugs are not overaged, then a major possibility lies in the EGR valve. When your EGR valve sticks as a result of getting gummed-up, it causes temperatures in the combustion chamber to rise, and these high temperatures lead to pinging. Simply cleaning the EGR may eliminate the problem.
Look for the protective guards around the exhaust system They frequently come loose and rattle as you describe. Look for a shield over another shield (hiding one from your view)
On a similar note, inspect the catalytic converter shield. These almost always get a little stone in them and it drives me crazy until either it jumps out, or I go fish it out, or (done several times) drilled a hole in the protective guard to let stones out.