My PSA and free PSA have been rising but not consistently?

My PSA and free PSA have been rising but not consistently.
Had a biopsy 2 years ago that was negative.
PSA 6 months ago was 6.5, 2 months ago dropped to 4.35, and yesterday was 8.7.
Also had free PSA ratio done yesterday with was 8.6%.
No urinary tract issues I’m aware of or prostatitis symptoms.
Besides cancer, what can cause free PSA to be so low and PSA serum to
bounce around so dramatically?
Not taking testosterone or anything else. Prostate size is small – @25.