My experience (in multiple cars, albeit not your make/model) has been that this sound always means your cooling system is under-filled. If you've emptied your cooling system and refilled it, it can be really hard to get all the air pockets out of the heater core, especially since in many vehicles it's almost as high as the radiator cap and at the opposite end of the system. The best system I know of is to park on a steep grade with the front of the car facing upward, then let the engine run with the radiator cap off. Squeezing the hoses, especially the hoses near the back of the engine compartment that go to the heater core, and varying the throttle can help. You should get bubbles coming up the top of the radiator. Whenever the fluid level drops, add some more coolant, and repeat until you can't get any more bubbling.

By the way, another symptom that might indicate this is your problem is that it's usually associated with poor heater performance (taking a long time to get heat, or only getting warm air, not hot air, out of the heater).

Sloshing Sound Under Dash
I have an old cheap keyboard which spans 5 octaves plus one extra C, so it goes from C2-C7 (I think).

Does that make this a 41 (5 x 8 +1) key or a 61 (5 x 12 + 1) keyboard?

When we talk about a standard 88-key piano is that the total number of white and black notes, meaning it covers just over 7 octaves?

While I'm here, what are the standard keyboard configurations if any other than a traditional piano can be said to be standard?
