Oh sure. I see you looking at me via the Internet spycams *waves*. I'm knocking back my third cup of coffee and you're thinking, "This woman needs to comb her hair and does she know she still has toothpaste drool on her chin?" Let's put that aside for now. *wipes chin*
La Trobe University in Australia has released a study claiming that participants knocking back copious amounts of coffee (five cups or more a day - child's play) and under stress may hear things that you won't find on Pandora -- like your seventh grade teacher asking for your book report on the worm reproductive cycle. The study asked test subjects to listen to white noise and indicate when 'White Christmas' by Bing Crosby was played. Those with higher levels of caffeine and subjected to more intense stressors (not listed but I'm assuming a five-year-old was involved) were found to boogie to Bing even though the song was never played.
So how does this relate to ghosts? If the investigator is highly focused on finding something - and hopped up on coffee during the night - are they really likely to hear a voice float out from the ether? Or is it the combination of caffeine and the brain making them more susceptible to suggestion?
Or does the caffeine make them more receptive? Hmmmmmm, they didn't cover THAT angle, did they? (not the purpose of the study)
Like any good study, more research is needed. I'll keep you in the loop as always.