Hi Bo/Half Bike: regardless of gear 1,2,3,4, when I step down on pedals, the gear seems to slip, then catches, then slips than catches. At first this only happened every once in a while. I just took the bike out for a spin few minutes ago and it does it everytime on the downward push of the pedals. Any ideas what this can be or how to address? Thank you for the generosity of your time.