How do you show a wolf howling in a comic book panel if the wolf isn't visible? In some movies, you see a shot of a mountain and you hear wolves howling in the distance, perhaps behind the camera. How do you do this in a comic panel? The issue is that you should maybe use a text bubble, but then the text bubble doesn't point towards anything. How is this normally done? Are there other alternatives?
Sounds in the distance are spelled over the backdrop
When a sound happens off screen, and out of dialogues, the sound or words simply float in the frame, like this:
This happens to be a ghost, if you can’t guess. But a roar, or even speaking detached voices can float over the frame.
If the sound comes in dialogue but off screen, you point the bubble out of the frame (cut the point of the spike flat, so it is clear the point extends beyond the frame.
Excuse the quick mockup, but perhaps something like this? This method puts the sound effect in a bubble that is shaped like or gives clues to what is making the sound. This kind of thing could also be done in varying degrees of style, such as only using ears on a bubble or doing a full drawing. .
I would suggest showing a panel with a silhouette of a wolf howling --perhaps closely zoomed in to the muzzle if you don't want to confirm that it's really a wolf (ie, might be a werewolf). Then you could follow up with a panel showing the sound effect echoing through the woods. You could even have characters reacting to it in fear, if that's the atmosphere you want to convey to the audience.
My rationale is that even if the wolf isn't present in the scene, comics often need to exaggerate visuals to communicate extra information that would normally be present in audio (ie, no soundtrack means the background colors change to indicate mood). And using a silhouette helps to communicate that the wolf might not physically be there in the moment, while still evoking the concept of a wolf howling.