Your question has landed in the MS community but i think i might be able to answer your question.....stomach growling and lower abdomen spasms/vibrations can actually happen at any time because of the digestive process. After eating the muscles contract to push and churn the food and liquids down the digestive track, air and gas also get squeezed, which is what creates the noises.
Then around 2 hours after eating hormones are produced to stimulate local nerves to send a message to the brain to restart the process and signal the digestive muscles, these contractions then deal with any remaining food that was missed and the vibrations of an empty stomach will make you feel hungry until you eat again.
Loud rumbling can mean your stomachs empty, it can also mean the foods you've eaten are producing more gas, and it can also indicate gastrointestinal issues like IBS but generally you'd be experiencing other gastrointestinal complaints and not just a loud growling lower abdomen if there was a gut problem.
Hope that helps.....JJ
Your question has landed in the Multiple Sclerosis community. There is a community for women with PCOS. You can find it here.
http://www.medhelp.org/forums/Polycystic-Ovarian-Syndrome-PCOS/show/203