my amp (fender blues deluxe) is sporadically making explosion noises, making it unplayable. i've never changed the tubes, had it around 3 years; could a blown tube be the problem? none of the tubes are actually smashed or anything, and it doesn't look like there's and exterioir physical damage.

any ideas?

yeah, time for a tube change, especially if the tubes are 3 years or older. Did you buy it new or used? Generally depending on use, current production powertubes will last a year or 2, preamp tubes usually last twice as long as power tubes on average.
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Sounds like a new pedal effect to me you should market it....

And joking aside, it sounds like your tubes, most power amps get about max 2-3 years use before they start to go and maybe one of them went out with a bang instead of dieing a slow quiet death.