For the last day and a half, I've had tinnitus in my right ear that sounds like a large diseasel engine idling in the distance. Happened last week too, and I spent a fair bit of time trying to locate the source of the noise before it randomly stopped.
As tinnitus goes, it's probably about as un-annoying as it gets[1], but it's not helping me hear or sleep, leading to general grumpiness. Also, if I wanted my life to have a diesely rumble as a soundtrack (rather than computer fans, as dog intended) I'd have joined the Navy or something.
[1] Certainly preferable to my brain trying to pick out distant voices from the noise floor, which seems to be its usual silent room trick.