Engine cooling fan ISX

[Big red 09]

Was wondering if AC had something to do with it. I have had truck shut off with key on and no signs of air. I have had fan switch on and off of course with engine off to actuate fan and then grabbed blades and no loose movements. Also took belt off with clutch engaged and spun it and tried rocking back and forth and again feels tight and solid
The belt was slipping when the fan clutch is having its fit because when this is happening it’s not fully engaging. So in essence it’s like you are restricting air to fan clutch but not all the way so fan is trying to come on partially and when it’s doing this the belt is gonna slip as the clutch is partially locking up or could be the friction surface of actual clutch disc making the noise. I have turned heater controls off as this happens and nothing changes either (no defrost heat air etc)
The idea that seals may seal after warming may be something. I would think that would do this as soon as truck started in morning but it takes a warm up and about ten minutes of driving before issue starts? I believe the fan clutch needs 100 psi of air to release and I don’t believe it is a two speed
Over the years it’s always either been on or off when working properly