I always wondered if Overcooling of the condenser, with too much fan, was possible, in mild ambient temperatures.
My fridge compartment is adjoined to another cabinet. This cabinet now has my original 2013 era Noctua NF-f12 exhausting both.
I put the Noctua A12x15, (only 15mm thick) on my condenser a few years back and at that point moved the nf-f12 to adjacent cabinet.
The extra 10mm space behind the fan compared to 25mm thick fans, it was hoped, would help the degree of flow through the fan and reduce noise further. This was successful in the noise department. I did not take before and after duty cycle data with this second fan switch.
The A12x15 draws about double the amperage of the NF-f12,but which is still less than the sleeve bearing fan provided with the fridge.
This 0.05amp NF-f12 Noctua fan, and their non industrial versions, come with one or two 'noise reducing adapters', which contain a resistor inline on the cable which slows the impeller rpm, reduces noise and amp draw.
This 0.05 amp load, with no resistor cable inline, is insignificant enough, that I just run it 24/7, rather than have it switch it with the compressor.
So This second fan now draws air, through my condenser, then across my compressor and compressor controller, even when the fridge compressor is not running and the A12x15 is pushing air into the condenser.
In winter I run the slowest 'noise reducing cable' adapter, in summer I take it off for the full 1500 rpm@12vdc.
My system works awesome, but I wonder if I am shortening the Fridge ( VF c51is) lifespan by having ventilation across condenser and compressor even when the compressor is not running. the ~15 minutes off, but with 50cfm of air being drawn around the compressor, likely has it swinging through a wider temp range, even if it never gets quite as hot as it would without the second fan always pulling air through condenser/across compressor.
Your 92 to 120mm adapter likely moves the fan far enough away from the condenser fins that it does not cause the impeller blades to stall, which makes the fan sound like it is spinning faster, as it becomes louder when it can't efficiently scavenge air from behind it.
My opinion is that mounting a computer fan directly to pull air through a radiator/ condenser, with little to no space behind the blades and fins, is asinine design.
I've not used such an adapter (92 to 120mm), but I experiment
with all sorts of computer fans all the time. They ALL are quieter when there is no restriction immediately behind the impeller, and ALL are quieter, and move more air, when pushing into a restriction( condenser/radiator) rather than pulling it through.
If a fan grille/ finger guard has to be used, moving it just 5mm farther away from the blades yields surprising improvements in noise and airflow, and mo distance is mo Betta, upto a point.
The closer the restriction is to the spinning fan blade, the louder it gets and the worse it performs, but pushing into a restriction is always much better than pulling, on the dozens of fans I have experimented with. The only difference is the degree, but it is always significant.
My 2013 era Vitrifrigo c51is came with a sleeve bearing fan, rated for 72 cfm but did not list a static pressure rating, iirc.
When I first got it, i was running it, using it normally, but outside the cabinet which I had to modify, as it was built for a norcold De-0040, which is slightly shorter and exhausted out the top faceplate. When the NF-f12( ~53 cfm, but high static pressure rating) arrived, I took duty cycle data, before removing the VF provided fan and then seeing the On/OFF cycle times when I installed Noctua NF-f12, orienting it to blow into the condenser.
It went from ~ 5.5 minutes on and ~15 minutes off to ~4.75 minutes on to ~15 minutes off, and was quieter, and the fan itself drew half what the fan VF provided with the fridge.
The VF c51is is a front loading 51 cubic liter( 1.8 cubic foot) fridge with the cooling unit on the top back of the unit. I made a cooling unit 'tunnel' from the failed Norcold's door skin to not only protect the cooling unit from installation/ removal
stress/ impact, but to also insure the fan's full flow went not only through the condenser, but also across compressor and compressor controller, and then into the adjacent cabinet, with no possibility of being recycled through condenser.
I also lined this 'tunnel' with some Butyl rubber roof flashing, with Nashua Flexfix 555 tape covering the sticky edges. This helps dampen the noise of the compressor, somewhat.
The danfoss/secop bd35f compressor is so much quieter than my Sawafuji powered Norcold was, that this extra sound dampening was not needed.
The 72 CFM sleeve bearing fan provided with the VF c51is was louder than the compressor.
The Noctua NF-f12 mounted to condenser, to pull air through condenser was louder than compressor.
The Noctua NF-12 mounted to opposite side of the condenser, to push Air through it, was significantly quieter than the compressor.
The Noctua A12x15 mounted push where the NF-f12 did for 5+ years previously, was quieter.
My 2013 era danfoss/secop bd35f makes a clunk when the compressor first turns on, but after that, I cannot hear it. I only rarely notice the clunk nowadays, when all else is very quiet.
Your Video sounds like a horrible metal on metal sound, like some moving part within the compressor is touching that which it should not.
Is this noise coming from the compressor body itself, or from some other part of the portable/chest style cooler?
Can you change the noise intensity by tilting the unit, or putting a finger here or there on surrounding components?
You say the noise is especially bad when the compressor first fires up. Does this duration of noise, before getting quieter, change with ambient temperature?
If that horrid metal on metal sound is emanating from the bd 35f compressor body itself, I would not expect it to live a long life, and would expend little to no more energy in trying to make it quieter, unless tinkering is just in your nature.
If tinkering is, and the compressor noise intolerable, while that clocks ticks toward potential(likely?)premature failure, and...
With your fridge being a portable, you always have to be aware to not cover the cooling unit's vents. One could build a spot for it that can perhaps dampen the sound, but still allow, or even perhaps enhance, ventilation through the cooling unit.
Dual ball bearing computer fans are awesome, much better than sleeve bearing fans, though when new and still lubed well, the sleeve bearing is usually quieter for the same sub 1800 rpm.
The hydrodynamic/ Maglev bearing types of fans are the quietest, and the longest lived, at least warranty wise.
in 2013 I asked Noctua about compressor vibrations and their 'SSO' bearing and they said it should not be an issue. It was/ is not.
I've used an accellerometer app on my phone
to greatly reduce noise and vibration from some high rpm Computer fans that are imperfectly balanced, but these are not fridge applications, and I've not experimented with the Noctuas in this regard. The IPPC 3krpm noctuas could have likely benefitted, before they all failed, as I recall
feeling then vibrate at high rpms.
While My condenser fan is now only 15mm thick, and the previous fans were 25mm thick, there are 38mm thick fans. Pretty much overkill for a fridge condenser in my opinion, but the thicker the fan the more static pressure and CFM it can generate for the same rpm.
CFM ratings of fans are in open air. No restrictions. I am told they measure the velocity of the air exiting the fan and do some math with fan diameter to come up with the rating they post as opposed to actually physically measuring the volume of air moved.
If one plays with a computer fan, one with 4 hub supports, they will likely find 4 hotspots of flow, exiting fan at wide angles. If this hotspot velocity is what is measure, and they do some math with fan diameter to come up with the CFM, then that cfm rating is wildly inaccurate/misleading in my opinion.
The static pressure rating of a fan, when mounted close to a restriction, is a much better figure, in my opinion.
The Noctua NF-f12 has only a 53 cfm rating, but in static pressure ratings, outperforms most other 120x25mm fans with a 50% higher CFM rating. The computer nerds loved the NF-f12 for its ability to keep their motherboards cooler for significantly less noise.