You may be getting an RF image/or "birdie" on your scanner. It could be internal to your scanner on that particular freq, or if it's outside interference it could be from a nearby electronic device. Example: Directv boxes emit a dead carrier right on KWHP's freq of 135.000, very annoying! CAT 5 Ethernet cables also emit carriers on the 6 meter band too, very annoying when listening to CHP freqs.
Try moving your scanner or antenna or simply putting on some snap-on type RF chokes on your coax, you can get them from Radio Shack or (even cheaper) at All Electronics in North Hollywood.
I get SOCAL on all 5 approach freqs fine from my location, have been contemplating hosting a "SOCAL approach" only feed for the valley, since the airports are covered pretty well now.