I have a neutered five year old female (D.K.) who makes a lot of noise in the spring and a neutered tuxtom (Hube) who gets very uptight about territory and ocassianal mounts (or tries to) my other cats. This behavior usually goes away cduring summer and I don't reinforce it by paying them any attention when it happens.
If a cat has been neutered by a vasectomy, snipping the tube that carries sperm to the penis, rather than a castration, total removal of the testicles then your cat may still feel "urges". Some catteries keep a "dud stud" around to pacifies females (queens) that they don't plan on breeding for a year or two.
Conversely, if a female cat has been neutered by having her tubes tide rather than an ova-hysterectomy - complete removal of the uterus and ovaries then that female will still experience esterous (heat).
Check with the veterinarian who preformed the procedures as to exactly what was done. If you don't know take them to a veterinarian for examination. Your vet may recommend futher surgeries or medication like buspirone. In the mean time, ignore them or fake ignoring for them. My cats will often "preform" for me for no greater reward than my attention. Are they preforming for you ????