DO they have bearnings.. YES. But another issue.. Give me some thought timne
A nest causes not so much knocking as fairly high speed vibration... But anything that causes an imbalance can do it too, but the fan and blower turn fairly fast so it is what I'd call vibration more than a "knock" but then.. You and I may define things differently So I will go with my syspect list.
Inspect the fan for any nicks or breaksm if a piece of a blade has broken off that will do it.. Likewise inspect for CRACKS in the plastic.
Do the same with the blower......
True story:
One Friday in August, early evening, I noticed my across the drive neighbor up on his roof looking at his Carrier Air V. HIs complaint was a RATTLE sound.. He fired it up and I confirmed.. Seemed to be coming from the blower end more than the fan so I showed him how to pull the inner cover (And assisted) he inspected the blower and it was ..... Cracked clear to the hub.
Late Friday. Nearest parts store 30 miles and likely closed even if they have it. nearest parts store likely to have it 100 miles.
I had one in my basement.. He was very happy
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times