Cat Meows

I have a cat who's 8 years old.  He's never been aggressive to any house guest, but lately when my mom visits he will be all sweet and rub on her (excessively) and then he will start this loud meowing.  He hasn't hissed or growled at her, but it stresses me out and I get scared.  I usually close her in a room if this happens and get him upstairs.  He's also done it to me once.  My mom isn't afraid of him, but I'm nervous that he could attack her? I've heard cats don't attack unprovoked, but I'm just wondering if I'm overreacting to his meow and if I shouldn't show my fear.

Any advice would be wonderful.

Thanks,

What kind of loud meowing?

My kitty babies sometimes meow very loudly, but it's because they want attention. As soon as I look over they give me a "do you love me?" face and I go pet them. If I don't, they meow loudly again every couple of minutes until I pet them and / or pick them up 

It's hard to describe, but it's between a loud meow and a howl, if that makes sense.  He's got his sweet meows and he is part Siamese so he is a talker, but when this meow comes out, it's different.   It's like he's upset about something, but again has never hissed or shown his teeth.  It's the same kind of meow as when he see another cat outside (mine is an inside cat).  I guess I'm just protective of my mom and don't want her to get attacked by him (she's been attacked by a cat).  She says she's not frightened so I'm just wondering if I'm overreacting to his behavior and just have to wait out if he does something.

Now with other guests, he doesn't do this.  My boyfriend comes over and he loves him to pieces. 

I haven't heard that kind of sound before. I'm sorry I won't be able to help there.

But, it would be good to see if your mom does something differently than the other guests. Maybe she wears a lot of perfume or a scent that kitty doesn't like. Maybe she sits in kitty's spot. 

If he's rubbing on her, it most likely means he's cat "marking" her with his scent. Apart from their booty, they have glands on their face and paws which they use to mark their territory. It very well may be he's marking your mom as his human and he "screams" for more attention from her or is speaking to her. Has your mom tried to safely meow back to her? I "talk" with the momma of my kitties and she always replies so we do this for several minutes back and forth. 

Maybe I can be of help based on experience. My boyfriends cat can be like that with me (we live together for 6 months now). The cat can be very affectionate with me and sometimes not, but I know when she doesn't want to be bothered. As for that noise, one day she was making that sound you described to me when I was on the floor organizing a book shelf. Thought she wanted my attention so when I went to go pet her she "slapped" me with claws. Just barely broke the skin. Then ran away. Now I take that sound as a warning not to go near her or pet her.