Rattle

[quadbimmer]

i need some help with a rattle.
i have got an '01 X5 3.0 with 102k

under hard acceleration i hear a distinct rattle like i have got quarters in the valve cover
the car does not make the noise standing still
or in park. and it doesn't tick at idle only under harder acceleration (like speeding up to change lanes, or other spirited driving)

i just got the car used, and i hope i didn't just get a limon.

any help would be greatly appreciated