If you let the "R" scan through the entire VHF band, it will stop on 156.000 MHz, whatever antenna you try, change location, ... S9 signal.
The "R" has an internal oscillator at 26 MHz. Since it is an SDR, it runs the receiver with square waves, so you're hearing the 6th harmonic of 26 MHz. There might be one or two on UHF too (the proof is left as an exercise for the reader).
By the way, the diagram published on the Yahoo! Group mentions a 13 MHz oscillator, while I'm holding right now a UV-3R board with 26000 (kHz) oscillator right next to the RDA chip. I've also found a difference on VHF and UHF mosfets, to be documented in another post.