Question from a friend

[simpo two]

Hi folks, I haven't been in here before but I have a question you might be able to help me with:

A friend of mine has a M reg Audi A4 that has a deaf car radio. A known-OK replacement has been tried but same result, virtually no received signals. We think this model used the heated rear screen as an aerial along with a pre-amp. Does anyone know if this is correct and if so, where abouts is the pre-amp located?

Thakns in advance :)