It's funny you should say that, Anderegg, because I seem to notice this a great deal on the analog talkgroups. For instance, listening to ALS Palomar I can have a nice clear signal on one frequency, but if the carrier drops and picks up on another freq, the signal will crackle and pop : ) I have not taken notice of which frequencies this happens on, but it looks like it might be worth it to pay attention next time and maybe keep track.
By the way, my research on the FCC site found these locations for the 863.150 MHz control channel:
Red Mountain, Fallbrook 33-24-01.1 N, 117-11-27.1 W
Black Mountain, Poway 32-58-53.2 N, 117-06-59.1 W
San Marcos Mountain, Vista 33-12-53.1 N, 117-11-18.1 W
4.5 miles WSW of Ramona 33-00-32.7 N, 116-58-21.2 W
Lake San Marcos Peak, San Marcos 33-06-40.1 N, 117-12-08.1 W
Soledad Mountain, La Jolla 32-50-23.2 N, 117-15-09.1 W
Campo Graves, Campo 32-36-04.2 N, 116-28-39.1 W
Encina Power Plant, Carlsbad 33-08-12.1 N, 117-20-14.1 W
Hubbard Hill, Escondido 33-09-09.0 N, 117-04-42.0 W
650 Benet Hill Rd, Oceanside 33-13-31.1 N, 117-21-59.2 W
85 Encinitas Blvd, Encinitas 33-02-53.9 N, 117-17-31.0 W