87 B2000 - whirring and loss of power

HI,
Have this weird problem with my truck. It just started making this loud whirring sound that is one to one with the gas.
Meaning the more gas I give the truck, the louder the whirring gets, or spinning drill sound, but at idle, the truck sounds fine. There has a also been a loss of power under load, like acceleration or going up hills etc. but once cruising along at speed it is fine except for the loud whirring sound.
Any ideas? It;s been happening for about a week and it's the same, hasn't gotten any worse.
Need some idea before I take it to a shop which I can't really afford right now.

Thanks everyone!

Will it make the noise if you're running the engine in neutral?
If so, check it in your driveway, to see if you can narrow down the area of the engine that its coming from.

Yeah, it does, I've tried that.
But it only whirs when I'm giving it gas, not idling, neutral or not.
And I haven't had the chance for a friend to come over and give it gas while I have the hood up.

Anyone of any ideas?

You shouldn't need another person...
Just twist the linkage at the carburetor with your hand.

Oh yeah, haha.
Anyways, I figured it out. I took the middle hose off of the three hoses going into the bank at the front of the carb. And it runs great now. Guess something is in there all clogged up, or isn't there reed valves in there or something? IS that emissions stuff? I'm new to this truck and to mazda's.
thanks-

You got a plugged rear catalytic convertor.