2002 sts

I just purchased a 02' STS. The guy I bought it from changed the brakes himself and didn't replace the brake pad sensor. I've found them on the internet and they're relatively inexpensive but I was wondering are they difficult to put on. Also, when I turn the wheel while moving there's a little knocking noise in the column. A mechanic told me that it's a rubber boot on the steering column that runs along side of the exhaust pipe that goes bad on these cars sometimes. I'm trying to get second opinion! Does anybody no anything about either of these issues?

Thanks