RV-9A with a Garmin 300 GPS/COMM. Began having comm static in proximity to towered airports. Within 2 miles of airport instant static that lasts until 1/3 to 1/2 mile from landing. Squelch has no effect and it seems to only occur on lower freqs below 123.0. Upper freqs are OK. Static does not build in intensity - it is either there or gone. RMI? antenna mounted on top of fuse just behind canopy (slider). Any ideas anyone? Do not have the problem at my home base (non-towered).