Amplitude demodulation on receiver receiving higher frequency than initial message tone
Your RC time constant appears to be too long for envelope detecting a 1 kHz sine waveform correctly. This will produce audible harmonics and may give the impression that the tone is higher pitch: -



470 kohm and 1 nF produce a 3 dB cut-off of 339 Hz. Try lowering the 470 kohm to something like 47 kohm.

Fix this first then see what happens.