What if the little green Italian sports car, happened to resonate at 433. MHz?
And, with a reasonable Q? Then, your weak 3rd harmonic, will retransmit from
the sports car and your receiver will pick it up. I contend that it is your Tx
output filter that is not performing. Do a conducted emissions test (not the
powerline type but the RF type) using a spectrum analyzer and filters and
attenuators to measure your actual output to the antenna. At a minimum you
should see at least -60dBc as required by the FCC, for any spurious emission
(97.307(e))
Hans
