Honda Car Forum

Hello,
I don't know a lot about cars, but this forum looks really helpful. Hope you will be able to advise:

My 98 honda civic DX hatchback started to sound somewhat like an old mustang after I drove over a big bump in a parking lot. My dad got under there and said that the pipe is broken right before going into the catalytic converter. So, we had someone weld it together, but 300 miles later it's doing the same thing.

I'm wondering:
1. Can anyone recommend a good muffler shop in the Bay Area in order to get this fixed?

2. Is it better to replace the whole pipe (not sure what this is called)? Meaning, the pipe that goes into and out of the catalytic converter, or just that specific section?

3. It is not making a lot of noise, but just a noticeable change to me. Wonder if it is really necessarry to do anything immediately? Or can this wait approximately 1000 miles until I drive back to Los Angeles next summer and go back to the place that originally welded it?

4. My dad was concerned that the gas tank seems to be covered with a sort of grease. The place we took it to said that this is normal, and if there were some sort of gas leak we would smell it, but my dad says that if it were really an oil leak, the whole underside of the car would be coated, and not just the gas tank. What do you think?

Hope this makes sense.
Thanks in advance to anyone who is able to provide some insight,
Jenny