I have a very simple city bike. I have neglected it outside for a while to a level I had to take it to a repair shop manually because of a blown tire. At the shop the tire was changed and the breaks readjusted.
But now when I am riding it I have a very loud cranking clanking sound (like the chain is hitting something, or something similar, don't know where it comes from) coming when I don't pedal for a few meters (for example going down a hill). It will go for a few more meters and stop, and then again. It barely happens when I am just leading the bike with my hands (it will continue if this sound started, and I got off the bike for a while, but then disappear), it also doesn't appear when I pedal.
I can't find the source because the sound is only on when I am on it and disappears when I am off it.
What could it be?