I have been having trouble with fan noise -- a noisy, rapid thumping sound, especially on startup but getting worse over a few weeks and lately persisting all day. Following this excellent guide, I removed the fan and examined it. I could see nothing wrong except perhaps a fine layer of dust on the blades, no worse than could be expected. I did not manage to disassemble the fan itself, as its two-part housing is very firmly clipped together, but applied a vacuum cleaner hose to both the entry and exit sides to clean it up as much as possible. I put it back and reassembled the whole display, and am pleased to report that the noise has completely disappeared. This may be good news to anyone dismayed by the apparent non-availability of replacement fans.