Pusb

My MGF has started making a very strange sound. I'm hoping someone on here recognises it! Its intermittent, but when its there its very loud. It does change pitch with RPM, but not in a direct correlation (if that makes sense?)Being in gear or out of gear makes no difference, nor does having the clutch engaged or disengaged. Speed makes no difference. Any ideas what it could be? Its louder on the passenger side. I was thinking possibly the fuel pump?