Pinging noise from underneath car

[Drks1de]

Hey guys, I'm new here, well to posting anyway. I've got this pinging(?) (sounds like marbles banging around in a glass jar) noise coming from underneath my car. It only does it when I give it gas, and only when the car is in motion. Also seems to do it more when i've been driving for a while, when the car is warm. It's been doing it for about 1 1/2 - 2 yrs now. First I thought it was my cats, had them replaced and and the O2 sensors and it wasn't them. Them I thought it was my Corsa cat back, replaced that with the Loudmouth 2 and it still does it. Anybody have any clue as to what it might be?? It gets to be very annoying. And I know that I shouldn't be doing this but, I do run low octane gas in it. The car is a '01 T/A and is stock except for a ram-air hood, ws6 air lid and a Loudmouth. The car has about 77,000 miles on it. Any help would be greatly appreciated. Thanks guys.

[ws62001]

Using low octane gas in a car that clearly states in the owner's manual to use Premium = . Your car is detonating. Do a search on it.