Hey chaps

I newly got a 01 RSV Mille and just yesterday after a 2hour drive i left the bike like 1 hour and after that i got a nasty sound possibly from the intake system like hving a hard time sucking in the air and at random times it gives a backfire when holding steady revs. After i came home i thought i heard some minor clicking as well but not sure about that.
Opened the air box filter and found some gas sprayed inside so it definatelly is backfiring.. now the million dollar question is what can have been wrong while the bike was standing..
Hope to get some light on the case