Wierd noise...97 Jetta Trek (Any help?)

[Timetogetill7]

I have a 97' Jetta Trek and for a while now I've noticed a short strange sound, almost like a circular saw sometimes when I turn and accelerate.

Any idea what it could be? It started just a few weeks after having my brakes changed. Don't know if they could be the cause. I figured it would eventually go away, but it hasn't and something tells me it's not a good thing.

Also how much does it usually cost to remove and weld in a new muffler?