About the audible noise of capacitor
When subjected to an electric field, Dielectrics expands in the direction of the field and contract in a direction transverse to the field.  The strain varies roughly with the square of the electric field.  Most materials have electrostrictive strains on the order of \$1*10^{-7}\$ for Electric field strengths of \$ 1 \frac{MV}{m}\$.  In Perovskite oxide materials the strain is \$ 1* 10^{-3}\$ at the same field strengths. Data comes from *(1) which seems to be highly cited.

While \$ 1 \frac{MV}{m}\$ seems to be unreasonable, a simple plate spacing of 1 um and a drive of 1 volt can easily meet this Field. So a normal capacitor with a 100 nm gap and 10 Volts being driven can easily exceed that number by 100 X.

For a capacitor that is say 1 mm in a given dimension a \$ 1 \frac{MV}{m}\$ Field would cause expansion by about 1 angstrom (0.1 nm) and probably more than 100 X that.

How much of that couples into an audible sound is hard to tell, but US patent # 7689390 B2 uses 100's of nm thick BST (\$Ba_{0.7}Sr_{0.3}TiO_3\$) layers to couple electrical and acoustic modes for a capacitor.

PTFE (Teflon) has high electro-restrictive coefficients. *(2)

So it does look possible.



(1) "Cracking in ceramic actuators caused by electrostriction"
W Yang, Z Suo - Journal of the Mechanics and Physics of Solids, 1994 - Elsevier"

(2) Schwodiauer, R.; Neugschwandtner, G.; Bauer-Gogonea, S.; Bauer, S.; Heitz, J.; Bauerle, D., "Dielectric and electret properties of novel Teflon PTFE and PTFE-like polymers," Electrets, 1999. ISE 10. Proceedings. 10th International Symposium on , vol., no., pp.313,316, 1999