Noisy blower motor but not the blower motor

[jw4821]

I've got a really annoying noise coming from what I originally thought was the blower motor, but after swapping the motor for new it's still there. 

It's a very faint high pitched noise that changes with the speed of the motor and stops when it's on zero. 

I've changed the blower motor for a brand new one and the noise persists. 

It almost sounds like something is catching, however if I remove the motor from the housing it sits in and turn on the blower I still get the noise so I'm sure nothing is catching on the new motor. 

I can't think of anything else downstream it could be. Anyone had anything similar to this before?

Video available here

[LukeC]

Faint noise?! That's a pretty loud squeak/high pitched noise! To me it sounds like something rubbing, or there's something in the vent tubing rustling around.

[jw4821]

Sounds louder than it is with the camera being so close. Once the trim is back in place and the road noise kicks in it’s not as bad.

I’ll have another look at the weekend, this time inside the tubing. I’m not sure what would get stuck for this long as it’s been like it for a while!

[LukeC]

Years ago, I had an issue with a leaf, and receipt that got picked up from somewhere. Eventually they worked up to the dash blowers facing the driving seat so managed to get them out from there. I can't say for sure that's the issue with yours, but might still be worth a look.

[ffrenchie]

On full power open the vents one at a time and run through the control knob positions likewise to see if it dislodges something.

[Drummond]

To me that video sounds normal   That only slight "rubbing" noise I can hear mostly on speeds 1-2, I'd expect is coming from the brushes rubbing on the commutator. I.e. normal electric motor sound.

But I'm not saying there couldn't be something else going on. If you can remedy the noise, please report back. I have the same noise, and would not mind mitigating it if feasible.

In some other cases I have had high pitched sound because of flaps or duct joints leaking. The air is whistling in those orifices. But in that video I cannot hear such.