I just got home, and for about the last 2km I was hearing a weird sound coming from the back area. I let the bike idle in the parking lot, and the sound was definitely coming from the muffler. It's hard to describe, it went something like putt-putt-putt-putt (non-stop). When I placed my hand by the muffler I could feel strong puffs of air hitting my hand - one at a time, with a tiny pause in between (maybe 2-3 per second).
I didn't have this noise before - it was consistent.
What could be the problem? What could I check out?
Thanks in advance.