I reckon it could be what 31t®um said, a loose chainring bolt.
Take em all out, clean them and re-grease them and then tighten them to buggery
I had a similar problem to you, exhausted all other possibilities and then found out it was the chainring bolts. Only problem is that you said it was coming from the left crank arm
I reckon it could be what 31t®um said, a loose chainring bolt.
Take em all out, clean them and re-grease them and then tighten them to buggery
I had a similar problem to you, exhausted all other possibilities and then found out it was the chainring bolts. Only problem is that you said it was coming from the left crank arm