re noise coming up when freq inceaase,
seems to say capacitive reactance has decreased,
the noise looks like various mixture of radios and what not coming from electric common ground into the circuit enclosure, not seeing the schematic and cannot hardly try desoldering caps or changing value when they are surface mounted.
this would require a peg board or caps attached with alligator clips with the culprits removed,.or not placed yet on protoType.
not now looking at the circuit,.
as you know, when we shunt signals to ground, existing the same path back into the circuit from ground,
(ground, where all of the noise is) unless we have an absolutely clean ground,. not likely with all of the raido not ,i say again my last, radio,over,
on the air,out. ground is a giant antenna.
surely you know how to test tone circuits of this type at least aproximate= aye figured . again good job! well done! friend wayne here in San Francisco