Direto X belt whirling noise

[bouzaskostantinos]

Hi there!
I own a Direto X and i'm having a "strange" whirling noise, i suppose from the belt, a noise like one that comes from a car's belt BUT only on High wattage(+300Watt) low cadence efforts (50-65rpm).
I want to ask:
1) can i try spray the belt with a specific belt silicon spray?
2) can i check the tension by myself?(though looks ok)
Any advice please?
Thanks in advance