Revving sound at highway speed- intermittent

[Pulelehua]

New to me '02 X5 3.0 has a troubling sound that I am trying to fix. I am the second owner, car has extensive maintenance history at 124k miles.

Yesterday, while driving at highway speed, my X5 made an intermittent sound revving sound. At first I thought the noise came from someone revving thier engine near me, or who had removed the muffler nearby.

My RPM'S were not surging, the car did not downshift at the time of the noise.

The noise would kick on for a few seconds mostly as I (slightly) accelerated at 40-55mph highway speeds.

I changed the oil the day before this sound appeared.

I am also replacing the purge valve today , p0444 & 44 selinoid valve tank ventilation code.

Any troubleshooting tips would be helpful, I have a BM700 bmw specific code reader, it does do live data.

Where do I start?

[80stech]

It might be a good idea to have a second person in the car to help track down the sound when it happens, even better if that person is mechanically inclined. A recording might be helpful as well. As for the purge valve make sure you replace that only with OE.

[Pulelehua]

This may just be the AC fan, this is the first time I have used the AC. Thoughts?

Also going to check to make sure the oil filter didn't collapse.