I have no idea why this has developed.
Welcome to the forum. Sometimes it is hard to pin point to an exact cause of T.
There are many causes which can trigger or aggravate tinnitus including but not limited to drug reaction or side-effects from ototoxic drugs, ear wax build-up, ear or Eustachian tube infection or ETD, ear drum injury, fluid build-up in ears feeling pressured or fullness, sinus infection & congestion especially with a bad cold, TMJ, TTTS, high blood pressure or blood circulation problem, loud noise exposure or acoustic trauma/shock, head trauma & injury, neck injury or muscle problems, hearing loss, Meniere's Decease, barotrauma from sudden change of air pressure such as during landing & taking off on flights especially with blocked nose causing failure to balance the pressure changes, slapping of the ears, deep grief for the loss of loved ones, untreated sleep apnea, extreme, extended stress, anxiety & panic disorder, etc., etc.
For masking here are some suggestions:
1) Mask at bed time if having trouble sleeping, by using a sound pillow or sound machine with pillow speakers. There are good sound machine & pillow therapy systems like this one:
https://www.amazon.com/Sound-Oasis-...d-Oasis-Therapy-System-Speakers/dp/B00MH5HKTA
2) If you need masking on the go, try load an ipod with nature sounds or music using itune. If you have a smart phone, you can download free APPs for soothing or T-masking sounds. Use wisdom in the use of headphones or earbuds as extended use or excessive volume may hurt your ears. Try set the volume slightly below that of your tinnitus.
3) With PC & speakers, you can try these excellent masking sounds to see which one masks best:
TT's excellent audio player:
https://www.tinnitustalk.com/audioplayer/
or this online sound library, particularly the self-mix nature sounds:
https://mynoise.net
or download free sound generator 'aire freshener':
http://www.peterhirschberg.com/mysoftware.html
or click play to mix these sounds with this simple sound generator:
http://asoftmurmur.com/
or search youtube with words like 'tinnitus masking sounds', 'white noise', 'rain sound' etc.
Good luck. Take good care. God bless.