I never noticed this before
 

This is the first time I noticed this but my wife pointed out that The rear side window behind the drivers side rear door window has an antenna in it.
The rear side window behind the passenger side rear door window does not.:dunno: Ok I'm stumped, What's that antenna for. :dunno:

The radio.

Guess I need to be checking it out to see why radio reception isn't as good as it could be.

Time to clean the windows, huh? ;)

Wouldn't it be nice if that was the problem....:nanana:..:rofl:

Someone stole the antenna on passenger side...:D ....
:jk:

Radio reception has been a problem on BMW vehicles for years. AM and FM bands have had problems.

Some tints applied to windows reduce reception.

The antenna booster units in the rear quarter storage areas can malfunction.

Radios in E53 models have been replaced under warranty for poor reception.

MD posted a TSB from BMW on replacing the radio due to customer complaints for AM reception. It is in the articles section IIRC.

The antenna coax leads in the rear can develop bad connections, and reduce reception quality.

It comes down to BMW having decided to incorporate a low gain antenna, and thus create a situation whereby any small problem with connections or receivers can be very obvious. But that antenna certainly is sleek, isn't it? Form over function, unfortunately.