[CJ_Boxster]

The 51psi marked on ur tire is the Maximum tire pressure not to be exceeded, it's not a pressure recommendation by the tire manufactor, take down the pressure to around 36-37 psi and fronts to 32psi.

For instance, when the tire says 51psi Max. That means 51psi=very high, 52psi - Up=danger of tire failure. The max isn't a pressure recommendation, it's just a warning not to exceed that pressure.

As for ur thump, set ur tires to our recommendations then go for another drive and check for noises again and let us know if it's still there