Fan tapping when engauged

[5150dieseltech]

It sounds like blade tapping on fan shroud. Not engine overhead or rod knock,nothing hitting fan,good clearances around it. When around 2000rpm when is fan on,does it and fades away when fan disengages. Fan is not wobbling, won’t do it parked under same conditions. No cooling problems and a/c is working correctly. Won’t do it all the time.
Sounds same as tapping blade with wrench. Any ideas ? I’m saying it’s fan noise, might not be ? I know it’s a questionable viscous electronic setup.

 

[Tuesdak]

Check the wires in front of the fan for hitting. Take belt off and check all the bearings for anything funky.

 

[5150dieseltech]

Connector attached to hub does move somewhat,not hitting. channel routing wiring to hub is clear of fan. Good call on checking tensioner and pulleys. I’ll check, initial checks for movement on hub and pulleys found tracking correctly and no movement but still should remove belt and check. I’m thinking it’s internal in hub when electrically engaged. It’s intermittent, comes and goes with fan on/off. No cracked blades found. I’ve worked with viscous fan hubs on cars, air actuated hubs on heavy duty. Never seen electronic viscous hub,don’t know how internals work.

 

[DonFitzwater]

What kind of truck are you working on? No signature so some information might help.