noise in ford fiesta engine - important?

hi, my 91 ford fiesta is making a horrible noise,

i located the problem to the engine, there is a belt that is attached to the starter motor, the area with the problem is on the actual engine it has 3 bolts in it, these bolts were LOOSE! when i tighten them the noise go's.

can i just tighten them up or is this a serious problem?