Ultrasound Vegetable Glycerin homogenization We are trying to homogenize VG (USP) with propylene-glycol using ultrasonic homogenizer with titanium probe, but we are experiencing very strange - bad odor from the emulsion after sonication. 
We tried different amplitudes, different time settings, different power settings. We can control amplitude for 2 modes only, I believe they are 50% and 100%.
Also if I am sonicating pure vegetable oil for just 5-10 sec I can smell that strange odor, it is very similar to that, I am getting with VG.
I just want to know, what this smell can come from? From our probe? No it is clean, we can sonicate water well.
Depending on intensity, ultrasound can produce intense heat at some locations. In fact, cavitation can induce temperatures far exceeding 5,000 K. Even a small ultrasonic room humidifier can burn through a plastic comb held in the upwelling stream. The sound intensity is decomposing the oil and/or propylene glycol.

Try lower frequencies and lower sound intensity. You might experiment with different shape containers, as well, to avoid focusing the sound into a high-intensity spot.