Thank you to all of you that replied!
I got the tape adapter after getting burnt with a "reputable" FM transmitter, a Belkin Tune Cast Auto specially designed for the Ipod. Spend €55 in it and it won't properly work, plus no chance of returning it. There are way to many radio stations in my area, so finding an empty frequency is next to impossible, and if I do, then you lose it after driving a couple of miles.
Like some one pointed out, before going for the GROM adapter, I wanted to try a cheaper solution, the tape adapter. And I have to say I thought I had hit jackpot with it the first time I plugged it in. The sound was very good, much better than the FM transmitter, but then came the bad surprise, the radio unit keeps spitting the adapter and it gets to be too annoying. I will try what someone said about the turning wheel in the adapter, and if that is not it, then I will have to go with the GROM.