A player on my server called a heli in and one of the rockets from the heli was lodged in his base making the hissing, just fired noise. So I deleted the rocket. But the noise is still there and it's filling my RustAdmin console with constant : 

(10:48:52) | InvalidProgramException: Invalid IL code in FlameExplosive:Explode (UnityEngine.Vector3): IL_0041: brfalse.s IL_ffffffc5
(10:48:52) | InvalidProgramException: Invalid IL code in FlameExplosive:Explode (UnityEngine.Vector3): IL_0041: brfalse.s IL_ffffffc5
(10:48:52) | InvalidProgramException: Invalid IL code in FlameExplosive:Explode (UnityEngine.Vector3): IL_0041: brfalse.s IL_ffffffc5
(10:48:52) | InvalidProgramException: Invalid IL code in FlameExplosive:Explode (UnityEngine.Vector3): IL_0041: brfalse.s IL_ffffffc5

How do I fix this? 

Restart server.

An IL error like this means there is an issue with the Oxide build you are using; simply restarting your server is not a solution. We'd need to know which Oxide build you are on to start with.

Yeah, I found the issue. My server host has these two buttons right next to each other and I accidentally updated using the Oxide Dev build ..... Did the steam update and patch oxide one and it's all working good again. 

Thanks, will have to disable that hook in the builds again for the time being. Surprised nobody else reported it yet.