engine noises

[gmtruck88]

After my brother's '94 chevy truck was rolled, we purchased a 95 with a bad motor and swapped. THis motor always ran very strong, even with 220,000 on it. After putting it in the 95 we noticed a squeal coming out of the exhaust. After we attached the rest of the exhaust system to the truck, it became quieter, but still very noticable. It seems to be worse when the engine is under a load, like when accelerating hard. Although i am fairly good with motors, i am stumped. it has to be something inside the motor but I'm not sure what. Any help would be greatly appreciated!