AM Radio Reception

[mauricio]

I have a 2009 TDCi Mondeo.
AM radio reception is very average. I've put up with it for some time but I'd like to fix it, if I can.
I listen to 693 3AW. Strangely, the station works fine in the morning at about 8:30am - little interference, static etc. But when I use it after midday it's terrible and I don't know what's causing it. How can it work fine in the morning then a few hours later it's awash with interference, noise etc. Has anyone else had this problem? Is it possible that they (3AW) reduce their transmitting power at a certain time of day to avoid other RF issues ?
I was blaming the car's radio (Sony) and have done the usual antenna and connection checks but given that the reception is ok at certain times of the day I'm not so sure that it's my radio or antenna.