98 S-10 loud vibrating noises

Just recently my 98 S-10 2x2 pickup started making a loud vibrating noise coming from the muffler area. I checked but it's not the muffler. It happens mostly at about 13-1400 rpms and then at around 3800. Any ideas what to look for????

Does the sound get worse with rpms or with mph? As it shifts and you get up to about 40 or 50, what does it sound like? If it is happening at 13-1400, what happens when you throw the truck into neutral? What type of noise is it? Is it a whine, a rattle, a thump? Does it have some sort of rythym to it or is it a random noise or knock?

It;s your Cadallitic Converter. [spelling]. I have the same thing happening with mine right now. I drilled a hole in it, illegal, took something out, then welded it back up, brand new!

The sound is a LOUD vibrating sound. It gets worse as the engine works harder...up steep hills, and as the rpms get low, lugging. No rhythm, just random. I've been told it could be catalytic converter. Some have said drill a hole and "take something out" then weld back up. What do I take out???

What did you take out after you drilled the hole in the catalytic converter? I'd like to figure this out without relplacing if possible.