Noisy interior blower fan

[Lubrown]

Hi all, after a bit of advice regarding a noisy fan - the hot/cold air blower for the cab interior.

When turning the fan on it is normal volume for about three or four minutes but then I get a constant and fairly loud noise, almost as if there are a load of dried leaves in the ducts.
If I switch the fan off and straight back on I get another three to four minutes of almost silent running (in speed one anyway, the other speeds are noisier as you’d expect) then it starts getting noisy again.
If I don’t turn it off/on the noise will stop after about ten/fifteen minutes…only to restart three to four minutes later!

I have had the pollen filter out several times and tried vacuuming the opening. I’ve changed the filter too. I’ve kept an eye on the intake in the plenum chamber and only had to clear the grille of a few leaves once - we don’t have to park under a tree usually.

Is there some obscure place debris could gather and take a while to reach the fan blades and cause noise or is it a bearing in the motor or even some electrical issue?

I checked similar threads but didn’t see an issue like the one I have.

 

[Big Al]

Could be the motor bearings worn. They get out of balance due to the wear and cause a noise.

 

[Beano1989]

I’ve just got this, yet to have a look I’ll keep an eye on here

 

[Lubrown]

I’ve noticed the noise is guaranteed to start as soon as I reverse too. But it stops when I move forward.
I might have to start taking bits apart and see what happens.

 

[Rob1978]

I’ve noticed the noise is guaranteed to start as soon as I reverse too. But it stops when I move forward.
I might have to start taking bits apart and see what happens.

I believe the fan reverses when the van reverses due to the exhaust being located under the van this prevents fumes being drawn into the vehicle

 

[Paynewright]

I believe the fan reverses when the van reverses due to the exhaust being located under the van this prevents fumes being drawn into the vehicle

I believe the system switches to re-circulatory when reversing ie just moving around the air inside rather than pulling air from outside.

OP - did you fix it? I’d try the pollen filter first which is a PITA to do but not as bad as pulling the heater out! When I changed mine at the normal service interval I was surprised at the amount of crud / leaves in there!

 

[Lubrown]

I believe the system switches to re-circulatory when reversing ie just moving around the air inside rather than pulling air from outside.

OP - did you fix it? I’d try the pollen filter first which is a PITA to do but not as bad as pulling the heater out! When I changed mine at the normal service interval I was surprised at the amount of crud / leaves in there!

Still not fixed it. I’m on my third pollen filter - one I did myself and took time to ensure the air ducts either side were clean and one done during a service (forgot to tell the garage not to bother so they binned my charcoal anti mould filter for a cheapo basic one).
I’ve had the plastic scuttle off and peered in through the leaf catcher (which has huge holes but that’s the way the OE part is designed), cleaned around there - still noise.
I’ve put off going further so far because it seems a bit involved. Not going to let the garage at it though as I expect the cost will be huge and the fan still works, just noisily.