Wierd noise at 90+

History: Ran a best time on the G tech of 12.26 at 118 back in June on my personal back road drag strip. ( previous best time was 12.92 before the 50lb injectors and TT chip) I know the mph is off and the g tech time is in question compared to an actual track time but it has served as a refferance non the less.
My big concern at this point is towards the end of this summer I could only manage a low 13 to high 12 second run in the same conditions. (same stretch of road, same temps, same everything)
The diff is lately I was getting a weird occilation when I got to the end of the run. Sounded like a wump wump wump noise about twice a second when I got to the end of a run.
If I were to guess I would think it maybe a tire rubbing or out of balance, or a u joint failing. Or who knows what?
In a nut shell any body get the wump wump wump noise or know what it is causing it? :confused: