do you have autohubs or manual lockouts?

 

is the front dirveshaft hitting a crossmember when you articulate making the noise?

 

Sounds like your having problems with your auto hubs not locking.

Switch to manuals.

 

they did not put auto hubs on 1990 f150s, i have manual, its not the front driveshaft because it does it in 2H also, it must be somethin in the motor, any ideas?

 

yes, they did put auto hubs on it. dont go around stating that as a fact! some had factory manuals, while others had one of two kinds of auto hubs. do not go stating that as a fact please.

 

ok i hear ya, but anyhow back to the noise in my front end?

 

killer, i am thoroughly confused... your original post says it's a front differential problem that happens when articulating, but now you think it's an engine problem and it does it in 2wd? does it do it when articulating but not moving? if so it could be something hitting the fan, such as the radiator (bad)