Anyone help.325i engine rattling..

[Mckin]

Hey my e30 325i has a rattle/knock in the engine.. On idle it's fine, when reving u don't hear it but holding steady throttle between 3000 to 4000rpm thers a rattling/knocking noise. I held it at the steady 4000rpm an pulled each coil lead off starting cylinder 1. When I got to cylinder 4 the rattling stops.. Any1 any ideas.. Big end bearing??