Neighbor complaints from HOA and have no way of proof

[Razul Wallace]

I have a tenant who lives in a 2/2 apartment with four neighbors. My unit is on the second floor, but two neighbors have complained multiple times about my tenant being too loud. I've dealt with multiple complaints from the HOA, however when I bring to my tenant, they reply "they are quiet". I have no way to determine if my tenant is too loud or the neighbors don't want me to rent my condo. Any feed back on a solution, would be gladly appreciated.