I think it can be a normal part of ovulation for some women, however, if this is a new symptom for you you may want to get checked out by a doc. I recently developed that same symptom about 6 months ago, where there were streaks of old blood in my CM only during ovulation. I told my gyne who recommended a pelvic ultrasound, and they found a large cervical polyp and two endometrial polyps. Going to have to get them removed before I can even think about TTC! Hope that's not the case for you and it's just due to the follicle rupture from ovulation, but any new or unusual bleeding should be checked out by a doc. HTH!!