This is similar to another post but not quite the same... At work, our ventilation system produces a constant low pitched sound - like a rumble - as well as the sound of air blowing through the vents. It's not very loud, we can certainly talk, even whisper to each other, but when it shuts off, it's like a huge weight off my shoulders. My ears don't really pop but there's sort of a slight "tingling" sensation - like when the blood starts flowing to a hand or foot that fell asleep. You can usually hear several people in the same room say "Ahhh" as in we are all glad the noise has stopped. I have worked in this location for over 10 years and in that time I have developed tinnitus which is probably attributed to a number of bad behaviors as a youth. But I was wondering if this constant noise could contribute to the decline in hearing? Also, that sense of relief when the noise stops makes me wonder if the constant noise adds to our stress levels?
Basically you are asking: (1) does the low-pitch noise affect my hearing sensitivity; (2) has the noise aggravated hearing loss acquired earlier in life; (3) if the noise can induce stress and (4) if the noise may cause tinnitus (kind of a hidden question).
(1) Is the ventilator noise damaging?: Noise-induced hearing loss typically occurs at high sound levels. Occupational safe noise levels are set at around 85 dB SPL (Nat. Stand. Occupational Noise). This is comparable to listening to traffic on a busy road from 10 meters away for 8 hours/day for 5 days/week (see wiki on sound levels), or a diesel truck at 15 meters going 64 km/h. If you can still talk normally, the noise cannot be much more than 60 dB SPL, which is normal conversational level (see sound chart). So the ventilation noise is not bad for your ears as it is well below 85 dB SPL.
(2) Does the noise aggravates present damage?: Similarly to the answer under (1), the noise is not loud enough to be regarded damaging even with existing hearing loss.
(3) Does it cause stress? As @anongoodnurse suggested: yes it causes stress, apparently. Every unpleasant sensation will do so to a certain level.
(4) Effects of the noise on tinnitus: Typically, tinnitus is caused by hearing loss (see cause of tinnitus) and the pitch of tinnitus often coincides with the lost frequencies (see cause and effect of tinnitus). So if your "bad behaviors" at youth refer to loud music, then it is probably noise-induced hearing loss that has resulted in a dip at your hearing acuity at 4 kHz (the 4-kHz notch). In effect, the tinnitus you are experiencing will be around this frequency and therefore high-pitched. As the loudness of the ventilator is too low to cause damage, it is probably unrelated to your tinnitus.
Noises over 75dB can cause temporary damage (temporary threshold shift), noises over 85dB can cause both temporary and permanent damage (permanent threshold shift). The size of the permanent damage depends on the intensity of the noise, the duration, and many other parameters e.g. genetics, antioxidants, time between two exposures, etc... For example daily 8h of 80dB is considered safe, while daily 8h of 85dB or 20mins of 100dB is considered unsafe. Tinnitus is a sign of hearing loss, so it can be both temporary and permanent.
You should measure the noise levels. For example install Sound Meter to your mobile phone. (The results can depend on the microphone. Most of the mobile phones cannot measure 100dB+ sounds, but I think this is not your case.) For example the ventilator of my computer is 35dB. I agree with Chris Stronks, that it is unlikely that your noisy ventilator caused your tinnitus or has any effects on it.
- A TERM PAPER ON NOISE - INDUCED HEARING DAMAGE
- 2013 - Noise induced hearing loss: Research in central, eastern and south-eastern Europe and newly independent states
Sound is measured in units called decibels. Sounds of less than 75 decibels, even after long exposure, are unlikely to cause hearing loss. However, long or repeated exposure to sounds at or above 85 decibels can cause hearing loss. The louder the sound, the shorter the amount of time it takes for NIHL to happen.
The limit of permissible noise exposure, defined as the maximal level which did not cause measurable noise‐induced shift in hearing levels of workers exposed to it irrespective of exposure years, was shown to be NR 75 or 80 dBA.
- 2013 - Noise-induced hearing loss in the 21st century: A research and translational update
At this occasion, a standardised noise exposure was applied (20 min, 200–500 Hz, 100 dBA) and the TTS at 4 kHz was determined during at least 10 min after exposure.
According to new studies continuous exposure to low dB (65-70) sound (which don't damage inner hair cells) can cause neural changes in sound processing. Constant noise can cause annoyance, concentration disturbance, etc... as well.
- 2013 - Effects of passive, moderate-level sound exposure on the mature auditory cortex: spectral edges, spectrotemporal density, and real-world noise.
People are increasingly being exposed to environmental noise from traffic, media and other sources that falls within and outside legal limits. Although such environmental noise is known to cause stress in the auditory system, it is still generally considered to be harmless. This complacency may be misplaced: even in the absence of cochlear damage, new findings suggest that environmental noise may progressively degrade hearing through alterations in the way sound is represented in the adult auditory cortex.
Here we show that exposing adult rats to structured noise at a sound pressure level of 65 dB, which is markedly below the broadly accepted safety level standard, results in behavioural impairments and substantially impairs the function of the auditory cortex. The strong deterioration in cortical processing of acoustic inputs is independent of the modulation rates of structured noises. Almost equally strong effects result from 10-h daily versus 24-h daily exposure regimens. These results indicate that there can be substantial negative consequences for the auditory system documented at the cortical level, attributable to environmental exposure to structured noises delivered under conditions that do not directly impact hearing sensitivity. These noises are deemed to be 'safe' and are often present in modern human environments.
A cross-sectional study in Nigeria  among children frequenting a school near a major road (noise range: 68-85 dBA) found at least some annoyance and concentration disturbance in 70% of the children. Fatigue and lack of concentration came forward as the most prevalent noise-related health problems.
I am a Noise Engineer and an Air-conditioning (Mechanical) Engineer, and it is my job to understand the effects of noise to our hearing capability. To start with an analogy, can you smell yourself on your pillow that you used for a long time (say 3 months)? You cannot, but a visitor who just borrowed your pillow for a night can smell it.
Now to answer the question directly, a "prolonged and constant" exposure to a low level noise, even less than 30 dBA (whisper), can cause hearing loss. Specific study showed that exposure to 40 dBA on specific frequency for 3 months will cause a hearing loss on that frequency. Notorious about this common occupational risk are those working in an improperly designed air handling system, those living/working a 2 km radius from a Wind Turbine, those living within a 1.5 km from a sub-station transformer, and many more.
What causes hearing loss is not the sound(pressure/level) itself, but the SOUND POWER. Power is a product of sound level/pressure/energy and TIME! A Firecracker is an explosion that has very high sound energy but short duration. A wind turbine sound has very low sound energy but very long duration. In effect, the product or result is the same.
I hope this has answered directly the question and put the issue to rest.