Minoxidil is vasodilator , it will affect blood flow or pressure changes in inner ear, so can trigger tinnitus but it's very rarest side effect of it, till tym only few people reported.
So my suggestion to stop for 1 week or 10 days and see the effect, your tinnitus is resolving or not.
Next Steps
thorough ENT examination needed, sometimes pressure changes in neck vessels also can cause, inner ear, middle ear any abnormalities, av malformation, tumor, drug induced , nerve weakness, rhinitis, ET block etc. so many causes of it.
Health Tips
Investigations are available to do like tinnitogram ,CT , MRI n angiography for rule out vascular abnormalities but better do it after advising by ent specialist.
my suggestion once stop minoxidil for atleast 10 days and observe any changes in tinnitus present or not.