I have a 1954 Chevy truck. It has a 6 cyl.250 engine. It also has an automatic transmission. Whenever I take off and give a good amount of gas there is a loud screeching sound and not a lot of power. Once it gets going it goes away. Few mechanics can't figure out what it is. It's not a belt issue, already ruled that out.1 mechanic said it sound like a metal scraping sound. Any ideas?