Hi Susanne

Your information is about right, a nice stainless exhaust will make the sierra sound a lot nicer and would give you a little bit more power

You can buy one new but they are quite a lot of money. You can pick up a decent magnex/mongoose exhaust off here easily

There are many decent traders on here, you've just got to make up ya mind what exhaust takes your fancy.

Concerning the rubbing has the car got standard suspension? if so a set a shocks might be in order if u fancy it

Smit