Bought this as my new work van does not have an input for my mp3 player.
Ive not used it with the AAA batteries, just in the van with the 12v cord and with that it works fine.
There is a little background noise, but nothing too noticeable when on the move. I drive around 150 miles a day, both motorway and rural roads and have not had to re-tune it once - I leave it on 107.9 and its great.
As already noted by 'zarneewoop', local radio stations can cause interference, but then my local one will block out Radio 1 as I drive by, so I dont see that as a problem.
The only criticism I have, is that the lead between the transmitter and mp3 player isnt long enough, but other than that its fine.
All in all, for the price its a great little gadget.