. Both of those are THE most common. Sometimes you can get away with one or the other but highly unlikely.
I changed the converter, flexplate, and bolts on my car and drove it about 100 miles. Then we went on a 70 or so mile trip and when I stood on it hard through most of 3rd gear comming up a LONG steep hill, something rubbed and it sounded like I threw a couple rod bearings. I guess it was over 100 mph worth of air under the car made the cover flex enough to make the bolts hit it. I had to pull the cover and tweak it a bit, PROBLEM SOLVED.
Check it out. It's probably just something dumb like that, or a loose bolt.

Don.