Bad Cat causing bad mpg?

[Bothe]

The cat converter on my 98 makes a loud like pinging noise when im in idle. I only get 9mpg so I was think that possibly my converter could be clogged? I guess i have two questions.
1: Is it possible that the converter could be causing my bad mpg?
2: Does that pinging sound mean anything or is it normal?

[kozal01]

Ive never heard of a cat making noise but a bad cat will absolutely ruin your mileage.

[cowboyupcuzick]

I agree ^^^ a clogged cat will kill your mpgs but I've never heard of it making noises..

blue 1994 f150 5.8L on 35in Goodyear wrangler MT/R's, cold air intake, flowmaster exhaust

[Bothe]

I'll take a video of it later an post it so you guy can hear it. It maty be normal, but it just sounds strange to me an I'm not 100% that's where it's coming from, but when I put my head under there it sounds like its coming from that.