Had a slow leak repaired and was plugged up. Now I get thumping

I would only be curious as to whether prior to having the tire plugged, if you added any kind of off-the-shelf product like fix a flat? If so then what needs to be done is to break the tire down clean out the inside of the tire and the rim then reinstall and inflate to proper PSI. The other thing I would ask is if you drove any distance on the tire while flat or very low because it's a good chance that if this were the case the side walls of the tire have been crushed and the integrity of the side-wall has been compromised.