"funny' place for a cap, I'm was certain I too [I read a similiar observation] noticed a buzziness from using a flat brown ol cap across Q2C/B, Mica's are cool, I put in a Poly Film I got from somewhere and it made a difference to.
Silver Mica's nice cause' they're 'closer' %age wise to the stated farad value, and may drift less, careful choosing of the small value, this takes high end off the clipping.
Poly film doesn't exhibit any [of the very slight] HF buzziness in the ceramic, in this position, and the difference might not even be noticed or liked with different units and applications.
For that capacitor you can probably get away with using a Polyester film or Polypro. film capacitor with no buzziness like is exhibited with cermaic capacitors.
You can sometimes go on eBay and buy 50 or 100 small Silver Mica capacitors for not very much cash
