Clicking or rattling noise under the hood when heat is on?

[BrianDye]

2006 V6, about 88k miles.

No issues, just a weird noise. I don't have my windows open often enough to get an idea of when it happens, but I cant really put a pattern on it. Sometimes its only when its cold, and hasn't been driven long yet, other times its done it even after 45 minutes of highway driving.

The heat works perfectly fine, front and rear. When I turn it on though, doesn't matter the fan speed, or what area (floor, vent, def, etc) it happens. Its just a clicking noise that goes with the RPMs. Its embarrassing being in a drive thru or something with a nice looking vehicle sounding like dog crap. If I turn the heat off, it stops within a second. I can turn it back on sometimes and itll do it for a short period, and then stop, and vice versa, sometimes it wont do it for awhile.

Im not familiar with what all is involved with the heating system that could rattle, any ideas?

 

[Flag Gibby]

So it's definitely in the engine compartment and not the dash? Is the heat on with the AC indicator lit up?

 

[BrianDye]

It's definitely not under the dash or in the interior. It's only audible with the window down, and when I'm next to a wall or something, it sounds like it's coming from the front end. The AC button isn't on, I'm leaving here shortly and haven't driven since yesterday morning, I'll see if I can find some more patterns for it like only heat and whatnot. I'll actually pop my hood too, hopefully it does it now that I'll think to check, lol

 

[Flag Gibby]

Off the top of my head, I am wondering if it is the electrostatic fan kicking off and on due to a low coolant level. Do you have any coolant leaks or no coolant in the overflow reservoir when the engine is cold?

 

[BrianDye]

I haven't checked in a week or so but I did have coolant in the overflow tank when it was cold last time I looked. (I was periodically checking because I had recently changed my thermostat housing which was leaking like a faucet)

Last time I was at the car wash, as I was finishing drying it up in the bay, it was cold outside so I started it up and had the defrosters going, and noticed the fan kicking on and off every 5 or so seconds. It was constantly spinning but would spin audibly faster for a short period then stop. I had plenty of coolant when it was doing that...