2012 bmw x5 35i e70 has 100k miles and a not so loud, but loud enough to notice in and out of the car, noise when idle or beginning to accelerate. It is springy in nature, a higher pitch, a little bit like a rattle. I was thinking like a rocker arm/ valve type noise on an older car. Or somesort of gearlike thing engaginh and disengaging in a cycle. When idle it is intermittent and doesn't change with heat or ac engaged.

It doesn't seem to affect my performance (but is a little embarrassing) and goes away as soon as I accelerate from a stop.

Theories or guesses to what itt could be?