[4.2L_Guy]

ok about 4 days ago my pickup started to squeek really bad when i am shifting down... and when i reverse... dont do it when i am accelerating...

then i hauled the 4-wheeler (about 800 lbs) out to 6 6 6 (sweet trail) and it didnt do it once... im thinking its a u joint... but y would it only do it when i let the clutch out when i shift down... or in reverse... i really need help guys thank you.