whistle or screaming noise....HELP!!!

I have a 1990 B2200. Fresh rebuilt motor that is stock on the outside. It ran great for the first 3000 miles and now it has developed a whistle or screaming, whizing noise. It is getting worse and is there when the engine is under load only. I can pump the gas pedal fast or slow and the noise gets louder at the speed of me pushing the gas pedal not the speed of the truck. It does it at all speeds. It also lacks or looses power unless I feather it. I think it has to be a vacuum leak somewhere but I cant find it. I have searched and sprayed and cant seem to find anything. HELP HELP HELP.......Thanks in advance you guys are always great.

Maybe a leaky intake gasket or gasket under the carb?

If you have a weber, the gasket for the adapter plates or the plates itself could be loose. Mine whistled untill I put some lock tight on the adapter plate bolts.

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<<<have the same problem except my motor is CLAIMED rebuilt....I dunno.....but I have a whisltling and its not REAL loud but I have to feather it most times or it gets chuggy atill about 3k rpms. weird. Oh but if I am on it with the gass...it seems ok. I really need that and my ac fixed...its getting hot out here and FAST!!!

he said when under load....mine is the same.....mine meaning when driving and in gear....be a lil hard for me to get a hose near the motor...and I tried putting it up on the lift and doing it that way.....didnt work....same if I had it on the rollers......it VERY frustrating

I will check the brake booster hose, Thanks I hadnt thought of that. I got the power thing fixed but still have the noise....It almost has to be vacuum related as the gas pedal effects it while under a load and nothing else. My noise is very loud and can be heard blocks away I am sure.....lol While at idle or coasting it seems to go away.....I WILL figure it out.....lol

Solution for the gutlessness when hitting the gears? I really need this to get fixed and SOON!

turbo is whistling. All that great horsepower. or, could be the muffler bearings.

I had the same problem with my weber plate. Tighten it up and no problem. With it running try and wiggle the carb and spray carb cleaner around the base to see if the idle changes.