Harmonic Balance/Propshaft weight Vibration

[udt123]

Hi all,

I recently got my harmonic balancer changed by a mechanic because there was a vibration every 2 minutes. After the change, I have a constant vibration (at idle) that can be felt from the steering wheel and pedal. The mechanic is now saying that it's the propshaft weight that needs to be recalibrated but he can't guarantee that it will fix the vibration because I have after market mufflers.

Does this seem plausible? Or do you guys think that the mechanic messed up the installation of my harmonic balancer?

Thanks for the feedback!