Note disparity between ears.

I perforated my right ear drum on a twig some years ago but it healed well and left me with mild tinitus. As a result of recent exposure to excess noise I have now lost a lot of sensitivity in that ear below about 300Hz and it has a sort of blocked feeling. The eardrum is clear on the outside and my eustacian tubes appear clear (visual observation of eardrum when swallowing thanks to a vet friend). Strangest of all at 1000Hz both ears hear exactly the same but below 800Hz down to 300Hz my right ear hears notes up to a semitone lower (tone generator with headphones) than the left at which point they come to hear the same note. Then below 300Hz the right ear perceives the note as higher until loss of sensitivity precludes further testing. (Two sets of headphones used and swapped ears etc to rule out equipment foibles). Effect dissapears over a couple of days until more noise exposure. Been going on for a month or two. Any idea what could cause this?
Thanks.