Looking Doubleboost's excellent vid on his new welder reminded me of just how noisy this fan is!!
I have a 3 yr old R-Tech 250i AC/DC welder and boy was this fan noisy.
while removing the plastic ends to clean out dust n dirt, I noticed that 25-30% of the impeller tip was blanked off!
so out came Mr Snips and off with the offending lumps ( warranty had expired, I couldn't wait.).
The plastic cover/louvre also got the chop as this was very restrictive to air flow.
while I was at it I decided to filter the air.
I probably could have made the filter smaller or a rectangle shape, but I reckon it helps with the noise attenuation.