Z4 2.2 ENGINE RATTLE WHEN COLD

[TIMZ4]

WHEN I START MY 2.2 Z4 FROM COLD IT STARTS IMMEDATLY WITH NO ENGINE NOISE BUT AFTER A MINUTE OR SO THE ENGINE SPEED DROPS AND IT SOUNDS "TAPERTY" UNTILL IT WARMS UP(AROUND FIVE TO TEN MINUTES)THEN IT IS FINE. IS THIS NORMAL?

THANKS

TIM SCOTT