I bought the aerial base from here ...
http://renaultpartsdirect.co.uk/products/Renault-Clio-197-Aerial-Base.html
HOW TO - Replace the aerial base
Note: This is a relatively straightforward job, you have to be prepared to wrestle with the headlining a bit.
1. Open the boot lid and you will see 2x clips on the headlining as shown below, these pull out whilst depressing the clip
2. Undo the middle seatbelt attached to the roof lining (16mm socket).
3.Pull the headlining down and behind where the circular magnetic thing is (that the end of the metal belt end makes contact with) , this will unclip out of the roof with a little pull. Removing this will give you better access.
4.Locate the right hand side of the parcel shelf area, there is a plastic unit which you can see below, pull the plastic clip off and then the plastic unit, this will then give you access to the end of the aerial lead (this leads back up to the aerial base)
5. You are now ready to hunt for the aerial base, familiarize yourself with the location on the roof of the Clio, to give you an idea how far down you will need to pull the headlining down to access. It will be nerve wracking doing this and you may think you may damage the headlining, however dont worry. I couldnt get a good picture as access is tight , however its up there somewhere
6. Using a 22mm socket you need to undo the base of the aerial, picture of the base below to help you identify what you are looking for.
7.Replace the aerial base with the new one and feed the wires down the same route as they were removed from. Hopefully this now solves your radio issues.
Checking your signal status
If you have an OE radio, you can check our ANTT status which gives you an idea if your aerial base is at fault. This is summarised below
Put radio in self test mode by pressing 1and 6 then i to test
Push the i button to cycle the test functions but look at the ANT number
ANT 8 to 9 is very good ANT 2 is poor poss aerial fault or fault with base due to corrosion
Taken from here (post #19)
http://www.meganesport.net/community/showthread.php?61014-Poor-radio-reception/page2