I've experienced a light bell sounds before that mostly comes from the right side of my bike when I'm riding (or so I thought it was from the right side) Here's some of my experiences. I hope it helps in some way.
1) 1st time I heard a ringing bell like sound when I rode was when my piston ring was loose. Only knew this when I went to the workshop and described what I heard. Mechanic revved my engine and said my piston ring is loose. He fixed it.
2) 2nd time I heard a constant bell sound when riding, I was afraid it was the piston ring loose again. But it shouldn't wear out so fast. When I slowed down the ringing stopped. When I sped up it came back. The second day, I found out that it was my keys hitting against my metal basket. #Goondu. I now have a leather keychain with my keys, it helps by not allowing my keys to hit or bump against my metal basket.
3) 3rd time I heard a ringing sound was a random day after working night shift. Heading home. A very weird ringing sound, more like a "cling cling" sound. Very constant. Also more to the right side of the bike. I didn't think it was engine problem, again when I slowed down the sound disappeared so I checked my keys. Nope, not the keys hitting anything. So I looked down at my basket nothing was there except my helmet bag.
But the sound would come back every time I sped up. Took me a few mins to find out that there was a penknife from work in my basket it was covered by my helmet bag so I didn't see it. #Goondux2
4) 4th time was when I went exploring in Lim Chu Kang area, passed a certain area that I thought I heard a bell sound. So I checked my keys. My basket was empty. I would randomly slow down and speed up to check, but the bell sound would be heard at random times. Only every now and then during that 2 hour exploring lim chu kang to Kranji, did I hear the bell sound. I hope that bell sound didn't follow you either. #Gdluck.