My APC UPS keeps making a buzzing noise?

[BillP]

I have an APC UPS and one of the caps - an SIEMENS EPCOS 20uF 150V Capacitor(datasheet:http://www.kynix.com/uploadfiles/pdf/B32232A3684K.pdf) - started making a buzzing noise.

This seems to be a AC, non-electrolytic capacitor and most local stores have it priced at ~$20 + tax.

They look like this: 

I also realized that caps of similar rating (20uF 250V) are present in the cheap pedestal fans they sell:https://www.ebay.com/itm/CEILING-FAN-CAPACITOR-CBB61-4-5uf-6uf-6uf-5-WIRE-/160824878870!

Those look like this:

Most importantly, these ones are also available on eBay for ~$5 and are worth a shot, but I had a few questions:

1. Is the buzzing because of the capacitor is bad or that a different component could be failing and having a secondary, audible effect on the capacitor?

   I thought the AC capacitors didn't have electrolytes in them and hence can't understand why they would be buzzing loudly when they did not previously

2. Should not both these caps be interchangeable in this application?

3. I am thinking of plugging out the 20uF 250V pedestal fan capacitor and putting this capacitor into such a fan instead, to confirm if the cap itself is causing the noise - sounds like a good idea?

   I am not sure why the fans use 250V caps but my assumption is that these Chinese makers just stock up on one variety of the caps since most of the world are at or below 250V.

   Hence, for this experiment, using a 150V cap instead of the 250V one for the fan (in the US) should not damage either fan or cap?

4. If it's confirmed that the cap's at fault, could I put in the 20uF 250V pedestal fan capacitor on the APC UPS board and expect it to have no detrimental effect on the UPS?

   My understanding is that this is a power cap and as long as the capacitance and voltage rating is good, other cap chars like ESR don't matter?

Here are pictures of the board:

 

It seems the noise is from the yellow cap, although there is a slight chance it could be from components around it (or because of malfunction of a component that's leading to the noise in the cap?).