To reiterate what globalhelper said in answer #1....BELT or TENSIONER . Get someone in the vehicle to turn the A/C on and off while you watch the accessory drive belt. When the A/C is turned on , your increasing the load on that belt IF the TENSIONER OR BELT are worn past there usable life expectancy (yes , both would be considered normal wear items), you will see and most likely hear the noise you're describing.Watch and see if the tensioner is vibrating back and forth rapidly , matching the 'fluttering' sound you're hearing.IF the noise is a knocking or ticking then we're in a whole different ballpark. Good luck.
Has anyone done a visual inspection as mentioned priorly? What did they notice?................7/25..been thinking about the 'flubbering. If not fixed already ..the A/C compressor could make that sound. Yes I understand , sounds are sometimes hard to explain.