Noise issues with two units..

We currently have two units that just don't seem to get along. One is below the other and the bottom one has consistently complained about noise from the neighbors above. To the point that the HOA has taken the time to investigate and nothing has been found.

While we do understand there is some noise that you will hear espcially being on the ground floor, the entire board almost doesn't take this complaint seriously as there has been other legal problems between the units, police called, etc etc.

The noise issue only seems to be the ground floor complaining. No noise has been witnessed by 3trd party. The owner recently decided to rent out the unit now her tenants are complaining. It appears to be unfounded and we have yet to have anyone else complain about this "noise". The owner has asked for noise testing.. which the HOA has denied, but offered if such is desired that the owner can pay for it independently.

Our HOA has had multiple contacts with the owner of the noise unit. We have yet to validate he reported noise and no other neighbor has said they experience such loud noises and disturbances etc etc. We have done our due deligence and have spoken too, met with and even had medation on these complaints, but the noise issues seems unfounded. We can't seem to catch anything and there is no real evidence of noise. The noise unit have all but said they are being harassed and legal measures are being sought. This sounds like a NON HOA issue and neighbor to neighbor. is it or is it not??