[ReelMagic]

I would suspect the horns themselves, see above from me regarding a service kit.... Had the same noise and suspected the compressor as well.  Figured out the diaphragms weren't working correctly which caused excessive noise at the compressor.. Know it doesn't make sense but once I installed the service kit the noise at the compressor went away... BTW if you remove the 3 screws on the top of the horn(s) you will find a plastic disc that vibrates when compressed air is supplied. Most likely the plastic diaphragms are worn out and/or the rim on the inside of the horn(s) has dirt/salt on it as well.. Clean completely and make sure the rim is smooth.. Not much work to do and it's a lot cheaper than a compressor. This problem re-occurs every few years and I go through the same process and its always worked... I know it needs to be done when the compressor makes a lot of noise.. M2C