i've had two gremlins rear their ugly heads lately in my E39 540
1. nav screen blank. i thought it was just kaputs, but there's power going to it with nothing displayed.
2. radio goes silent after 3 minutes. buttons still operate to change stations & such, but audio cuts out. i can turn it off/on again and i can get sound fine, but it cuts out after 3 minutes.
E90 2009 335i
retired: E21 1983 320is, E36/7 2000 M Roadster, E39 2000 540iA