@Spartan, I am nowhere near as adept at you with tech and diganosis, but in my experience sticking on 2 used different brand tread up front on my diesel (that takes 235 65 r17 all round) when initially installed, caused 5 mins of weird rumbling akin to driving over a relatively smooth cobbled road (that I wrongly putting do own to having more aggressive treads up front) this behaviour subsided BUT I noticed once when going up a relatively steep incline a shudder@1500rpm sort of like you have gone over a bad patch of road, and was even getting it on coming to a standstill in traffic so at lower revs.

I went purchased 4 new tires identical all good now.

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N