foamy bubbles in urine

I have type 2 diabetes and have bubbles in my urine,I thought it was protein in my urine,and they tested my urine and said a small amount was present,but normal for a type 2 diabetic.I mentioned it to another doctor,who also check my urine and said that yes a small amount was present,but that he thought it wasnt protein,that was causing it.Refered to another doctor who wants to go up my penis with a camara catheter,his thoughts it might be a fistula at the base of bladder that could be allowing air into bladder,My thinking is WHAT ,Is it me or shouldnt they be checking my kidneys,I mean Im not a doctor but thats what I would do,I guess that is what happens,but I think they all want to refer and test and refer and test,I will report back,but anybody heard of this a fistula causing bubbles in urine from a type 2 diabetic,kind of like checking your brakes when you go in with a fan belt noise.