I've noticed this recently in the Evo I bought a few months ago used.. I don't know if it's something I should be worried about or normal for this car? I've never heard a car do this before. It sounds like a metal "ping"/"ting" type noise when I let off the gas at low RPM.

 

Do you have a way to video record the pinging noise?

With what little info you are giving, I'm not sure if it's a "normal" noise considering your car has mods done. With my car at low RPM's and light throttle I can hear the engine doing it's thing... spark plugs firing. It sounds good.

When I let off the gas at low RPM, all I hear is a deep exhaust note that tends to set off car alarms. If there is a normal engine ping, I won't be able to hear it with my deep exhaust noise.

Record a video if you can. I'm sure someone can give some advice or experience.

 

It could just be some unburnt fuel hitting a hot downpipe and making a pinging noise. Mine will do so every now and then. Sounds more like a pop though.