I have an N54, Vanguard catless exhaust.....I torqued all the bolts and they seemed to be tight.
There is a DIY on the PS flush.....Didn't seem hard at all, similar to changing the oil in my car.
I haven't driven my car yet today, I'll see tomorrow if the noise on steering persists or eliminated.
'08 AW E90 335i
PROcede V5 | BMS DCI | RR DPs | ETS FMIC | FORGE DVs | Stett CP | Vanguard | PSS10