Thanks for trusting me to help you and Sarah today. I am a licensed veterinarian with over 30 years of experience and would be happy work with you.
Noise induced hearing loss is known to occur in people and in pets. There is not a lot of literature, but it is thought that in general, anything above 85 dB (decibels) can cause hearing loss with long-term exposure. Short-term exposure can cause damage at 120 dB. I don't know if a couple hours every 4 weeks would be considered long term exposure or not, but blow dryers would fall somewhere in the area of 70 dB, similar to a vacuum cleaner being run in the room. In thinking about chronic noise however, it is thought that a given noise for 2 hours causes the same damage as a noise twice as loud for 1 hour, so with frequent exposure over the years, I don't think we can say it may not have contributed some.
Dogs can also lose hearing due to other reasons. One is secondary to aging and is indistinguishable from noise induced hearing loss. Another cause can be secondary to chronic middle or inner ear infections and that is not able to be noted with just an otoscopic exam and more advanced imaging such as CT or MRI may be needed. Brainstem evoked response audiometry (BERA) is the technique most commonly used in veterinary medicine to measure degree of hearing loss. With this technique, the consistent changes in electrical activity in the brainstem following auditory stimulation can be recorded from scalp electrodes. It may be worth a referral to a veterinary neurologist for additional work up.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.
My posted replies are for general education only and not meant as a diagnosis. Only after a thorough veterinary examination can a diagnosis for your pet be made and specific treatments be advised or medications be prescribed.