Every once in a while, sometimes once a week, sometimes once a month just before i go to sleep i hear things in my head, mild auditory hallucinations, besides these hallucinations i have headaches every day, very strong headaches, more than 10 hours each day. Now i am going to take a PET scan to find the causes for the headaches and was wondering if at that exact time i am under the scanner and no headache is present and no hallucination, does the scanner still show anything that might be wrong with my brain?

Before I say anything I have to be clear that I am not expert about PET scan.

I would expect some difference of the scanned images between your headache time and no headache time. The reason may or may not be due to the headache itself, instead, may be due to the negative emotion induced by the headache. PET scan can show some of the affection of emotions.

Again, you should ask your doctor for this question.

I am no expert either, but considering that the difference in your pain level is possibly due to differences in your systemic inflammation level, the root cause could show up in a subdued state, but that's not a guarantee. There are lots of possibilities/factors.