Backfire

[Mal]

I have a 2004 model GSX1400. I have done thousands of miles on it fault free but now on heavy engine braking, I get a single backfire from the right-hand exhaust. Any thoughts on the cause? With gentle engine braking and using the brakes to slow there is no sign of a backfire. The bike runs well.
Best regards Mal.

[Hooli]

Balanced the throttles lately?

Sounds daft but if they are staying slightly open or more shut on the right it could be triggering the right conditions for a backfire when compared to the left.