Weird noise behind the dash

[Legacy777]

Ok....I've got some weird noise behind the dash. It's almost like something moving around back there, hitting plastic. The issue is that it seems to occasionally do that when the car is not moving, and fan turned off......that can only really leave on thing IMO.....something in the heater core. I have no idea what the hell could be in there. The heater still works fine, and I have no leaks.....so I'm a little confused.....

Anyone else have any other suggestions.

[vrg3]

It only does it when the engine's running?

[Legacy777]

yup....when engine's running only.....and I don't necessarily have to be moving. I mostly hear it when I come to a stop or when I'm not moving because it's a very faint noise.

[dzx]

I have that problem too. It stops when you turn on the vent system

[Legacy777]

I haven't noticed this in a long time. I think I had air in the system. that's about the only thing I could think of.

I think air was introduced because the coolant tank resevoir was below the L line....so it would suck air into the system rather then coolant. I filled the tank up, and bled the system and haven't noticed it.