I have purchased the vibrating egg, butterfly, vibrating panty and venus penis.

The egg is very quiet, but not as stimulating.
The venus penis and butterfly with insert are much more stimulating, but do make a bit more sound.

We have tested them a few times in public and not anything someone would hear. There are some realy cheap models that make lots of sound.

The other thing that helps is wearing tight Jeans. Keeps the vibrator close to body and in place better. They do sometimes move around when she gets wet.

She likes the Venus Penis and butterfly with penis(triple stimulators).