"Meeeh" is the sound leeches make. But since it developed by younger people, it is now the universal sound for practically everything. It is pronounced with a very squeeky voice.
Here are some examples:
Katy is trying to scare Jack. She is wating around the corner, and Jack walks by as Katy yells : "MEEEH!". Jack is startled.
Robert randomly says "MEEEH". Everyone laughs and proceeds to do the same sound.