I'm going to take some things apart this weekend and see what I can find. Where in the pictures are the diaphrams and how would I check them, any ideas?

The issue is more common now but I only notice it when I punch it on the highway. Through some other browsing I thought it may have been air in my cooling system since I've heard the glug-glug-glug watery noise behind my dash in the past. I bled the system as instructed and found no improvement to the current noise I'm having.

Does anyone have other ideas on my issue? Any chance it could be belt squeel, or an exhaust leak? My gut feeling is it's related to fluid or air flow.

Thanks gents.