Had, I guess means you didn't do it? Was it overfilled? Have you checked the level since? Has the airbox got contaminated with oil or is the stock paper element oil-soaked? Have you checked the drain hose?

Clutching at straws here though.

Can you think of anything else that was new, changed or done differently to the bike in the last few days?

When you say more noise, do you mean induction, mechanical, or exhaust type sounds?

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