Drivetrain 1988 mustang gt 5.0 rattling noise under acceleration

Lets eliminate the easy stuff first, but we need a little info to better help you, is the car stock or a few bolt ons? You would be surprised at the questions that have simple answers until there's the ' oh and it has a blower on it' revelation that will change everything.
what is the timing set at? Fuel pressure? Does it have the correct spark plugs, these are some of the things that will make it 'spark knock', you said it looses power when it 'rattles'. A hot engine will cause it to rattle and also a lean condition.
Oh, and always check for codes, that is the first step.